The Collaborative International Dictionary of English v.0.48:

Campion \Cam"pi*on\, n. [Prob. fr. L. campus field.] (Bot.)
   A plant of the Pink family (Cucubalus bacciferus), bearing
   berries regarded as poisonous.
   [1913 Webster]

   Bladder campion, a plant of the Pink family (Cucubalus
      Behen or Silene inflata), having a much inflated calyx.
      See Behen.

   Rose campion, a garden plant (Lychnis coronaria) with
      handsome crimson flowers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

campion
    n 1: any plant of the genus Silene [syn: silene, campion,
         catchfly]