The Collaborative International Dictionary of English v.0.48:

Oilseed \Oil"seed`\, n. (Bot.)
   (a) Seed from which oil is expressed, as the castor bean;
       also, the plant yielding such seed. See Castor bean.
   (b) A cruciferous herb (Camelina sativa).
   (c) The sesame.
       [1913 Webster]

WordNet (r) 3.0 (2006):

oilseed
    n 1: any of several seeds that yield oil [syn: oilseed, oil-
         rich seed]