phosphorus sesquisulfide

[ ses-kwi-suhl-fahyd ]
/ ˌsɛs kwɪˈsʌl faɪd /

noun

(not in scientific use) a yellow, crystalline, flammable substance, P4S3, insoluble in cold water and decomposed by hot water: used chiefly in organic synthesis and in the manufacture of matches.

Origin of phosphorus sesquisulfide