9 letters · 11 points in Scrabble
noun (KNO3) used especially as a fertilizer and explosive
originFrom Middle English saltpetre, alteration of Old French salpetre, from Medieval Latin sāl petrae (“salt of the rock”), named so being found as an incrustation. Alteration of the first element is from folk-etymological association with salt (which is, nevertheless, cognate to Latin sāl).
Etymology from Wiktionary, CC BY-SA 3.0