Noun
pneumonoultramicroscopicsilicovolcanoconiosis (uncountable)
(nonce word) A disease of the lungs, allegedly caused by inhaling microscopic silicate particles originating from the eruption of a volcano.
Ones like pneumonoultramicroscopicsilicovolcanoconiosis, of course. Source: Internet
The longest word in English is pneumonoultramicroscopicsilicovolcanoconiosis, a medical term. It's 45 letters long. Source: Internet