Longest word

Pneumonoultramicroscopicsilicovolcanoconiosis has 45 letters and names a lung disease caused by fine volcanic dust. It appears in major dictionaries, though it was coined to be long.

Context

The 45-letter word is defined in Merriam-Webster's medical dictionary as a lung disease caused by breathing in very fine silicate or quartz dust. Merriam-Webster's own writers describe it as the longest word in most standard English dictionaries.

It is widely said to have been coined in the 1930s, in part as a joke, by a puzzle enthusiast who wanted a word to rival the longest ones in the language. The word is built from Greek and Latin parts and is generally treated as a showpiece rather than a term doctors regularly use, since the standard medical name for the condition is much shorter.

Longer words exist elsewhere, such as systematic chemical names and invented words, but these are not entered in major general dictionaries. That is why the record is limited to words found in a major English dictionary.

Because the record is limited to dictionary entries, it is a matter of definition more than of language itself, which is why word-length trivia always carries qualifiers about what counts as a word.

Etymologically the word is a chain of parts: pneumono (lung), ultra (extremely), microscopic, silico (silicon or silica), volcano and coniosis (a condition caused by dust, from Greek konis, dust). Its meaning is a form of silicosis, which is a lung condition from inhaling fine silica, and the volcano element is largely a flourish.

Dictionary inclusion is a policy decision by editors, who generally list a word once it has appeared in use, even when the use is playful. Comparisons with other long terms depend on what is counted: chemical names for proteins can run to tens of thousands of letters, but they are systematic labels and are not listed as ordinary words, so the 45-letter entry is best read as the longest in this specific, dictionary-based sense.