The Collaborative International Dictionary of English v.0.48:

Papilionaceous \Pa*pil`io*na"ceous\, a.
   1. Resembling the butterfly.
      [1913 Webster]

   2. (Bot.)
      (a) Having a winged corolla somewhat resembling a
          butterfly, as in the blossoms of the bean and pea.
      (b) Belonging to that suborder of leguminous plants
          (Papilionace[ae]) which includes the bean, pea, vetch,
          clover, and locust.
          [1913 Webster]