Brit. sp. salt′pe·tre
Origin of saltpeteraltered (infl. by salt) from Middle English salpetre from Middle French from Medieval Latin sal petrae, salt of rock from Classical Latin sal, salt + petra, rock
See potassium nitrate.
Origin of saltpeterMiddle English salpetre from Old French from Medieval Latin sālpetrae Latin sāl salt ; see sal- in Indo-European roots.Latin petrae genitive of petra rock ( from Greek petrā ; see per-2 in Indo-European roots.)