salt ‧ pe ‧ tre BrE AmE British English , saltpeter American English /ˌsɔːltˈpiːtə $ ˌsɒːltˈpiːtər/ noun [uncountable]
[ Date: 1300-1400 ; Language: Old French ; Origin: salpetre , from Medieval Latin sal petrae 'salt of the rocks' ]
a substance used in making ↑ gunpowder (=powder that causes explosions) and matches