The Collaborative International Dictionary of English v.0.48:

Sinigrin \Sin"i*grin\, n. [From NL. Sinapis nigra.] (Chem.)
   A glucoside found in the seeds of black mustard (Brassica
   nigra, formerly Sinapis nigra) It resembles sinalbin, and
   consists of a potassium salt of myronic acid.
   [1913 Webster]