Merriam-Webster Collegiate Dictionary - mustard

 noun  Etymology: Middle English, from Anglo-French ~e, from must must, from Latin mustum  Date: 13th century  1.  a. a pungent yellow powder of the seeds of any of several common ~s (Brassica hirta, B. nigra, or B. juncea) used as a condiment or in medicine as a stimulant and diuretic, an emetic, or a counterirritant  b. slang zest  2. any of several herbs (genus Brassica of the family Cruciferae syn. Brassicaceae, the ~ family) with lobed leaves, yellow flowers, and linear beaked pods  3. a dark to moderate yellow  • ~y adjective