How very sesquipedalian!

Commonly cited as the longest word in English, the 1,185-character-long name for Tobacco Mosaic Virus, Dahlemense Strain in all its absurdity is:

Acetylseryltrosylserylisoleucylthreonyserylprolyserylglutaminyl
phenylalanylvalylphenylalanylleucylserylserylvalyltryptophylala
nylaspartylprolylisoleucylglutamylleucylleucylasparaginylvalyly
steinylthreonylserylserylleucylglycylasparaginylglutaminylpheny
lalanylglutaminylthreonylglutaminylglutaminyllalanylarginylthre
onylthreonylglutaminylvalylglutaminylglutaminylphenylalanylsery
lglutaminylvalyltryptophyllysylprolylphenyllalanylpolylglutamin
ylserylthreonylvalylarginylphenylanalylprolylglycylaspartylvaly
ltyrosyllysylvalyltyrosylarginyltyrosylasparaginylalanylvalylle
ucylaspartylprolylleucylisoleucylthreonylalanylleucylleucylglyc
ylthreonylphenylalanylaspartylthreonylarginylasparaginylarginyl
isoleucylisoleucylglutamylvalylglutamylasparaginylglutaminylgl
utaminylserylprolylthreonylthreonylalanylglutamylthreonylleucyl
laspartylalanylthreonylarginylarginylvalylaspartylaspartylalany
lthreonylvalylalanylisoleucylarginylserylalanylasparaginylisole
ucylasparaginylleucylvalylasparaginylglutamylleucylvalylarginyl
asparaginylthreonylphenylalanylglutamylserylmethionylserylglycy
lleucylvalyltryptophylthreonylserylalanylprolylalanylserine
(Can you believe Word’s spell-check confirmed this word!!)

Other lovely long words include:

Pneumonoultramicroscopicsilicovolcanokoniosis- a disease caused by the inhalation of fine particles

Antitransubstantiationalist- one who doubts the validity of transubstantiation

Antidisestablishmentarianism- opposition of those who oppose the link between church and state

Sesquipedalian is an interesting word itself. Said to be coined by Horace, it is a term for words so polysyllabic that they seem a “foot and a half long.”