( BrE ) ( US salt·peter ) / ˌsɔːltˈpiːtə(r); NAmE ; BrE also ˌsɒlt-/ noun
[ U ] a white powder used for preserving food and making matches and gunpowder
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WORD ORIGIN
late Middle English : from Old French salpetre , from medieval Latin salpetra , probably representing sal petrae salt of rock (i.e. found as an encrustation). The change in the first element was due to association with salt .