What does "mustard" mean?

Mustard: A powder or a paste made from the seeds of black or white mustard, used as a condiment and a rubefacient. Taken internally it is stimulant and diuretic, and in large doses is emetic. Mustard oil (Chem.), a substance obtained from mustard, as a transparent, volatile and intensely pungent oil. The name is also extended to a number of analogous compounds produced either naturally or artificially.