1. Honorificabilitudinitatibus

   The word consists of 27 letters. This word appeared in the script of Shakespeare titled “Love's Labour's Lost”, which means “invincible glorious.”

2. Antidisestablishmentarianism

   The word consists of 28 letters. This word means “opposition to the withdrawal of state support or recognition from an established church, esp. the Anglican Church in 19th-century England” as explained in Dictionary.com. It has been quoted once by the British Prime Minister, William Ewart Gladstone, 1809- 1898.

3. Floccinaucihihilipilification

   The word comprises of 29 letters. It means “act or habit to deny the value of some particular things.”

4. Supercalifragilisticexpialidocious

   The word comprises of 34 letters. This word appeared in a movie called “Marry Poppins”, which means “good.”

5. Hepaticocholecystostcholecystntenterostomy

   The word consists of 42 letters. It appears in the “Medical Dictionary” edited by Gao De as a surgical terminology, which refers to indirect artificial tube surgery between the intestine and gallbladder or in the gallbladder and bile duct.

6. Pneumonoultramicroscopicsilicovolcanoconiosis

   The word comprises of 45 letters. It appears in the eighth edition of Webster dictionary, which means “pneumoconiosis disease caused by inhaling small particles of quartzite.” Miners are particularly vulnerable to this disease.

7. Antipericatametaanaparcircum -
   volutiorectumgustpoops of the Coprofied

   The word consists of 50 letters. There is a display of one French writer's ancient story in a library shelf, with this long English word as its book title.

8. Osseocaynisanguineovisceri -
   cartilagininervomedullary

   The word consists of 51 letters. This is a terminology related to anatomy. It appeared in a novel called “Headlong Hall” written by an English writer, 1785-1866.

9. Aequeosalinocalcalinoceraceoa -
   luminosocupreovitriolie

   The word consists of 52 letters. This word was invented by the British Medical author, Dr. Edward Strother, 1675-1737. It is used to refer to the composition of mineral water found in England.

10. Bababadalgharaghtakamminarronn -
    konnbronntonnerronntuonnthunntro -
    varrhounawnskawntoohoohoordenenthurnuk

    The word of consists of 100 letters. It appeared in the book titled “Finnegan wake” written by Irish author, Andean James Joyce, 1882- 1942. This word refers to the downfall of Adam and Eve.
    

11. Lopadotemachoselachogaleokranio -
    leipsanodrimhypotrimmatosi -
    lphioparamelitokatakechymenokich -
    lepikossyphophattoperisteralektr -
    yonoptekephalliokigklopeleiolagoiosi -
    raiosiraiobaphetraganopterygon

    The word consists of 182 letters. This English word is derived from the Greece word, originating from the drama script of comedy titled “ecclesiazusae” written by a Greek writer, Aristophanes, 448- 385. It refers to spicy foods that cooked from the remaining vegetables and beef.
    
12. This word is terribly long in its length as it comprises of 1913 letters as follow:

    Methionylglutaminylarginyltyrosy -
    lglutamylserylleucylphenylalanylalanylglutaminy -
    lleucyllysylglutamylarginyllysylglutamylglycyla -
    lanylphenylalanylvalylprolyphenylalanYlvalythre -
    onylleucylglycylaspartylprolylglycylisoleucylg -
    lutamylglutaminylsErylleucyllysylisoleucy -
    laspartylthreonylleucylIsoleucylglutamy -
    lalanylglycylalanylasparthlalanylleucylg -
    lutamylleucylglycylisoleucylprolylphenylalanylse -
    Rylaspartylprolylleucylalanylaspartylglycylp -
    RolylthreOnylisoleucylglutaminylasPfraginylal -
    anylthreonylleucylarfinylalanylphenylalanylalany -
    lalanylglycylvalythreonylprolylalanylglutaminy -
    lcysteinylphenylalanylglutamylmethionylleucy -
    lalanylleuOylisoleucylarginylglutaminy -
    llysyhistidylprolylthreonylisoleucylproly -
    lisoleucylglycylleucylmethionyltyrosylalany -
    lasparaginylleucylvalylphenylalanylasparaginy -
    llysyglycylisoleucylaspartylglutamylphenylalany -
    lthrosylalanylglutaminylcsteinylglutamyllysylva -
    lylglycylvalylaspartylserylvalylleucylvalylalny -
    laspartylvalylprolylvalylglUtaminylglutamylsery -
    lalanylprolylphenylalanylarginylglutaminylalany -
    lalanylleucylarginylhistidylasparaginyvalylalany -
    lprolylisoleucylprolylisoleucylphenylalanylisoleucy -
    lphenylalanylisoleucylcysteinylprolylprolylaspartylalany -
    laspartylaspartylaspartylleucylleucylarginy -
    lglutaminylisoleucylalanylseryltyrosylglycy -
    larginylglycyltyrosylthreonyltyrOsylleucyl -
    leucylserylarginylalanylglycylvalylthreony -
    lglycylalanylglutamYlasparainylarginylalany -
    lalanylleucylprolylleucylasparaginylhistidy -
    lleucylValylalanyllysylleucyllysylglutamy -
    ltyrosylasparaginylalanylalanylprolylpro -
    lylleucylglutaminylglgycylphenylalanylglycy -
    lisoleucylserylalanylprolylaspartylglutaminy -
    lvalyllysylalanylalanylisoleucylaspartylalany -
    lglycylalanylalanylglycylalanylisoleucylsery -
    lglycylserylalanylisoleucylvalyllysylisoIeucy -
    lisoleucylglutamylglutaminylHistidylasparaginy -
    liSoleucylglutamylprolylglutamyllysylmethionyl -
    leucylalanylalanylleucyllysylvalylphenylalanyl -
    calylglutaminylprolylmethionlysylalanylalanylt -
    hreonylarginylserine.

    The above word refers to "Tryptophan synthase a protein", a chemical name for a substance that contains 267 kinds of amino acid enzymes.

     

(37) HEPATICO­CHOLANGIO­CHOLECYST­ENTERO­STOMIES = a surgical creation of a connection between the gall bladder and a hepatic duct and between the intestine and the gall bladder.
This is the longest word in Gould's Medical Dictionary.

(34) SUPER­CALI­FRAGI­LISTIC­EXPI­ALI­DOCIOUS = song title from the Walt Disney movie Mary Poppins.
It is in the Oxford English Dictionary.

(30) HIPPOPOTO­MONSTRO­SESQUIPED­AL­IAN = pertaining to a very long word.
From Mrs. Byrne's Dictionary of Unusual, Obscure and Preposterous Words.

(29) FLOCCI­NAUCINI­HILIPIL­IFICATION = an estimation of something as worthless.
This is the longest word in the first edition of the Oxford English Dictionary. Interestingly the most common letter in English, E, does not appear in this word at all, whilst I occurs a total of nine times. The word dates back to 1741. The 1992 Guinness Book of World Records calls flocci­nauci­nihili­pilification the longest real word in the Oxford English Dictionary, and refers to pneumono­ultra­micro­scopic­silico­volcano­koniosis as the longest made-up one.

(28) ANTI­DIS­ESTABLISH­MENT­ARIAN­ISM = the belief which opposes removing the tie between church and state.
Probably the most popular of the "longest words" in recent decades.

(27) HONORI­FICABILI­TUDINI­TATIBUS = honorableness.
The word first appeared in English in 1599, and in 1721 was listed by Bailey's Dictionary as the longest word in English. It was used by Shakespeare in Love's Labor's Lost (Costard; Act V, Scene I):

Shakespeare does not use any other words over 17 letters in length.

(27) ELECTRO­ENCEPHALO­GRAPHICALLY
The longest unhyphenated word in Merriam-Webster's Collegiate Dictionary (10th Ed.), joint with ethylene­diamine­tetraacetate (see below).

(27) ANTI­TRANSUB­STAN­TIA­TION­ALIST = one who doubts that consecrated bread and wine actually change into the body and blood of Christ.

(21) DIS­PRO­PORTION­ABLE­NESS and (21) IN­COM­PREHEN­SIB­ILITIES
These are described by the 1992 Guinness Book of World Records as the longest words in common usage.

Some say SMILES is the longest word because there is a MILE between the first and last letters!

(1,185) ACETYL­SERYL­TYROSYL­SERYL­ISO­LEUCYL­THREONYL­SERYL­PROLYL­SERYL­GLUTAMINYL­PHENYL­ALANYL­VALYL­PHENYL­ALANYL­LEUCYL­SERYL­SERYL­VALYL­TRYPTOPHYL­ALANYL­ASPARTYL­PROLYL­ISOLEUCYL­GLUTAMYL­LEUCYL­LEUCYL­ASPARAGINYL­VALYL­CYSTEINYL­THREONYL­SERYL­SERYL­LEUCYL­GLYCYL­ASPARAGINYL­GLUTAMINYL­PHENYL­ALANYL­GLUTAMINYL­THREONYL­GLUTAMINYL­GLUTAMINYL­ALANYL­ARGINYL­THREONYL­THREONYL­GLUTAMINYL­VALYL­GLUTAMINYL­GLUTAMINYL­PHENYL­ALANYL­SERYL­GLUTAMINYL­VALYL­TRYPTOPHYL­LYSYL­PROLYL­PHENYL­ALANYL­PROLYL­GLUTAMINYL­SERYL­THREONYL­VALYL­ARGINYL­PHENYL­ALANYL­PROLYL­GLYCYL­ASPARTYL­VALYL­TYROSYL­LYSYL­VALYL­TYROSYL­ARGINYL­TYROSYL­ASPARAGINYL­ALANYL­VALYL­LEUCYL­ASPARTYL­PROLYL­LEUCYL­ISOLEUCYL­THREONYL­ALANYL­LEUCYL­LEUCYL­GLYCYL­THREONYL­PHENYL­ALANYL­ASPARTYL­THREONYL­ARGINYL­ASPARAGINYL­ARGINYL­ISOLEUCYL­ISOLEUCYL­GLUTAMYL­VALYL­GLUTAMYL­ASPARAGINYL­GLUTAMINYL­GLUTAMINYL­SERYL­PROLYL­THREONYL­THREONYL­ALANYL­GLUTAMYL­THREONYL­LEUCYL­ASPARTYL­ALANYL­THREONYL­ARGINYL­ARGINYL­VALYL­ASPARTYL­ASPARTYL­ALANYL­THREONYL­VALYL­ALANYL­ISOLEUCYL­ARGINYL­SERYL­ALANYL­ASPARAGINYL­ISOLEUCYL­ASPARAGINYL­LEUCYL­VALYL­ASPARAGINYL­GLUTAMYL­LEUCYL­VALYL­ARGINYL­GLYCYL­THREONYL­GLYCYL­LEUCYL­TYROSYL­ASPARAGINYL­GLUTAMINYL­ASPARAGINYL­THREONYL­PHENYL­ALANYL­GLUTAMYL­SERYL­METHIONYL­SERYL­GLYCYL­LEUCYL­VALYL­TRYPTOPHYL­THREONYL­SERYL­ALANYL­PROLYL­ALANYL­SERINE = Tobacco Mosaic Virus, Dahlemense Strain.
This word has appeared in the American Chemical Society's Chemical Abstracts and is thus considered by some to be the longest real word.

(39) TETRA­METHYL­DIAMINO­BENZHYDRYL­PHOSPHINOUS = a type of acid.
This is the longest chemical term in the Oxford English Dictionary (2nd Ed.). It does not have its own entry but appears under a citation for another word.

(37) FORMALDEHYDE­TETRA­METHYL­AMIDO­FLUORIMUM
Chemical term in the Oxford English Dictionary (2nd Ed.).

(37) DIMETHYL­AMIDO­PHENYL­DIMETHYL­PYRAZOLONE
Chemical term in the Oxford English Dictionary (2nd Ed.).

(31) DICHLORO­DIPHENYL­TRICHLORO­ETHANE = a pesticide used to kill lice; abbrv. DDT.
It is the longest word in the Macquarie Dictionary and is also in the Oxford English Dictionary (2nd Ed.).

(29) TRINITRO­PHENYL­METHYL­NITRAMINE = a type of explosive.
This is the longest chemical term in Webster's Dictionary (3rd Ed.).

(27) ETHYLENE­DIAMINE­TETRA­ACETATE
The longest unhyphenated word in Merriam-Webster's Collegiate Dictionary (10th Ed.), joint with electroencephalographically (see above).

(26) ETHYLENE­DIAMINE­TETRA­ACETIC = a type of acid; abbrv. EDTA.
This word appears in Merriam-Webster's Collegiate Dictionary (10th Ed.).

(85) TAUMATA­WHAKA­TANGI­HANGA­KOAUAU­O­TAMATEA­TURIPUKAKA­PIKI­MAUNGA­HORO­NUKU­POKAI­WHENUA­KITANA­TAHU
A hill in New Zealand. This Maori name was in general use, but is now generally abbreviated to Taumata. The name means: the summit of the hill, where Tamatea, who is known as the land eater, slid down, climbed up and swallowed mountains, played on his nose flute to his loved one.

(66) GORSA­FAWDDACH­AIDRAIGODAN­HEDDO­GLEDDOLON­PENRHYN­AREUR­DRAETH­CEREDIGION
A town in Wales. The name means: the Mawddach station and its dragon teeth at the Northern Penrhyn Road on the golden beach of Cardigan bay.

(58) LLAN­FAIR­PWLL­GWYN­GYLL­GOGERY­CHWYRN­DROBWLL­LLANTY­SILIO­GOGO­GOCH
A town in North Wales. The name roughly translates as: St. Mary's Church in the hollow of the white hazel near to the rapid whirlpool of Llantysilio of the red cave. It is listed in the Guinness Book of World Records.

(41) CHAR­GOGAGOG­MAN­CHAR­GOGAGOG­CHAR­BUNA­GUNGAMOG
Another name for Lake Webster in Massachusetts. Probably the longest name in the United States. Alternative spellings are:
(44) CHAR­GOGGAGOGG­MAN­CHAUG­GAGOGG­CHAU­BUNA­GUNGAMOGG,
(45) CHAR­GOGGAGOGG­MAN­CHAUG­GAGOGG­CHAU­BUNA­GUNGAMAUGG,
(44) CHAR­GOGGAGOGG­MAN­CHAUG­GAGOGG­CHA­BUNA­GUNGAMAUGG.

(23) NUNATH­LOOGAGA­MIUT­BINGOI
The Eskimo name for some dunes in Alaska, according to The Book of Names by J. N. Hook.