The longest word in a major dictionary is 45 letters: pneumonoultramicroscopicsilicovolcanoconiosis.
This tongue-twisting term refers to a type of lung disease caused by inhaling fine silica particles. While it's rarely used in medicine, it was coined partly as a curiosity—and to be the longest word in the dictionary! Most people shorten or avoid it entirely, but it’s a favorite among word lovers and spelling bee aspirants. There's even a song that helps people say it without getting dizzy.