The Collaborative International Dictionary of English v.0.48:

Sinapis \Si*na"pis\, n. [L.] (Bot.)
   A disused generic name for mustard; -- now called Brassica.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Sinapis
    n 1: small genus of Old World herbs usually included in genus
         Brassica [syn: Sinapis, genus Sinapis]