The Collaborative International Dictionary of English v.0.48:

Sinapine \Sin"a*pine\, n. [L. sinapi, sinapis, mustard, Gr. ???:
   cf. F. sinapine.] (Chem.)
   An alkaloid occuring in the seeds of mustard. It is
   extracted, in combination with sulphocyanic acid, as a white
   crystalline substance, having a hot, bitter taste. When
   sinapine is isolated it is unstable and undergoes
   decomposition.
   [1913 Webster]