n.1. a. Any of various Eurasian plants of the mustard family, especially white mustard, Indian mustard, and black mustard, which are cultivated for their pungent seeds and edible leaves.
b. A condiment made from the powdered seeds of certain of these plants.
2. A member of the mustard family.
3. A dark yellow to light olive brown.
4. Any of a group of toxic organic compounds that include mustard gas and the nitrogen mustards.