It was coined in 1935 by American physician Dr. Everett M. Smith as a humorous attempt to create the longest word in the English language.
The word is made up of Greek and Latin roots, and it is intended to sound like a medical term, although it does not refer to any actual disease.
* Pneumono-: relating to the lungs
* Ultramicroscopic: extremely small, invisible to the naked eye
* Silico-: relating to silica (silicon dioxide)
* Volcano-: relating to volcanoes
* Coniosis: a condition caused by the inhalation of dust
Even though it's a fake word, its length and absurd nature have made it a popular example of the longest word in English, and it's often used for humorous purposes.