mustardyoudaoicibaDictYouDict[mustard 词源字典]
mustard: [13] Mustard was originally made by mixing the crushed seeds of various plants of the cabbage family with the freshly pressed juice of grapes – the ‘must’. Hence its name, which comes from Old French moustarde, a word derived from a descendant of Latin mustum ‘new wine’ (source of English must ‘grape juice’).
=> must[mustard etymology, mustard origin, 英语词源]
mustard (n.)youdaoicibaDictYouDict
late 13c. (late 12c. as a surname), from Old French mostarde "mustard, mustard plant" (Modern French moutarde), from moust "must," from Latin mustum "new wine" (see must (n.1)); so called because it was originally prepared by adding must to the ground seeds of the plant to make a paste. As a color name, it is attested from 1848.

Mustard gas, World War I poison (first used by the Germans at Ypres, 1917), so called for its color and smell and burning effect on eyes and lungs; chemical name is dichlordiethyl sulfide, it contains no mustard, and is an atomized liquid, not a gas. To cut the mustard (1907, usually in negative) is probably from slang mustard "genuine article, best thing" (1903) on notion of "that which enhances flavor."
I'm not headlined in the bills, but I'm the mustard in the salad dressing just the same. [O.Henry, "Cabbages and Kings," 1904]