Pneumonoultramicroscopicsilicovolcanoconiosis is a made-up word that's inaccurately used to mean a lung disease caused by inhaling volcanic ash. Despite the fact that it doesn't have an authentic definition, pneumonoultramicroscopicsilicovolcanoconiosis sounds very impressive when you say it out loud!
Leave it to a word puzzle expert to invent a word that still holds the honor of being the longest dictionary entry, at 45 letters. When National Puzzlers' League president Everett Smith coined pneumonoultramicroscopicsilicovolcanoconiosis in 1935, he intended to create the longest word, using Greek and Latin roots meaning "lungs," "beyond," "small-looking," "silicon," "dust," "volcano," and "disease." It would be a good name for such an illness — but nobody's ever been diagnosed with silicosis caused by breathing volcanic dust.