In a field of over 122,000 headwords,
pneumonoultramicroscopicsilicovolcanoconiosis beats out its closest
competitor (supercalifragilisticexpialidocious)
by 11 letters. Both have objections to them; the former was
deliberately invented to be the longest word in the language, and has
never been used in any other context, while the latter is an invented
nonsense word. Other, more legitimate, long words include floccinaucinihilipilification
and antidisestablishmentarianism.
One might also count trinitrophenylmethylnitramine,
and any number of chemical compounds whose names could go on for pages
if anybody cared to describe them that way.
