The Collaborative International Dictionary of English v.0.48:

Fissile \Fis"sile\, a. [L. fissilis, fr. fissus, p. p. of
   findere to split. See Fissure.]
   1. Capable of being split, cleft, or divided in the direction
      of the grain, like wood, or along natural planes of
      cleavage, like crystals.
      [1913 Webster]

            This crystal is a pellucid, fissile stone. --Sir I.
                                                  Newton.
      [1913 Webster]

   2. Fissionable.
      [PJC]

WordNet (r) 3.0 (2006):

fissile
    adj 1: capable of undergoing nuclear fission; "a fissionable
           nucleous"; "fissionable material" [syn: fissionable,
           fissile] [ant: nonfissionable]
    2: capable of being split or cleft or divided in the direction
       of the grain; "fissile crystals"; "fissile wood" [ant:
       nonfissile]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "fissile":
   alienable, breakable, brittle, brittle as glass, crackable, crisp,
   crispy, crumbly, crushable, delicate, dissoluble, dissolvable,
   divisible, fissionable, flimsy, fracturable, fragile, frail,
   frangible, friable, lacerable, scissile, separable, severable,
   shatterable, shattery, shivery, splintery, vulnerable