Pneumonoultramicroscopicsilicovolcanoconiosis

Pneumonoultramicroscopicsilicovolcanoconiosis [nyooh-mon-ah-ultra-mike-ro-sc-hop-ik-seal-i-key-knee-oh-sis] noun:
An obscure term ostensibly referring to a lung disease caused by the inhalation of silica dust, sometimes referred to as the longest word in the English language.
(origin; pneumono, ultramicroscopic, silica, volcano, (pneumono)coniosis)