pneumonoultramicroscopicsilicovolcanoconiosis
A facetious medical term for a lung disease caused by inhaling very fine silica dust, often cited as one of the longest words in English. In Japanese, it is a direct translation of the English coined word and is rarely used outside of word-length trivia.
"珪性肺塵症" is known as a translation of a very long English medical term.
A Japanese calque of the English word 'pneumonoultramicroscopicsilicovolcanoconiosis', composed of 珪 (silicon), 性 (nature), 肺 (lung), 塵 (dust), and 症 (disease).