The Collaborative International Dictionary of English v.0.48:

Bilateral \Bi*lat"er*al\, a. [Pref. bi- + lateral: cf. F.
   bilat['e]ral.]
   1. Having two sides; arranged upon two sides; affecting two
      sides or two parties.
      [1913 Webster]

   2. (Biol.) Of or pertaining to the two sides of a central
      area or organ, or of a central axis; as, bilateral
      symmetry in animals, where there is a similarity of parts
      on the right and left sides of the body.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bilateral
    adj 1: having identical parts on each side of an axis [syn:
           bilateral, isobilateral, bilaterally symmetrical,
           bilaterally symmetric]
    2: affecting or undertaken by two parties; "a bilateral
       agreement between the United States and Japan"
    3: having two sides or parts [syn: bilateral, two-sided]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "bilateral":
   Janus-like, ambidextrous, bifacial, bifold, biform, bifurcated,
   binary, binate, biparous, bipartisan, bipartite, bivalent,
   conduplicate, dichotomous, dihedral, disomatous, double,
   double-faced, duadic, dual, dualistic, duple, duplex, duplicate,
   duplicated, dyadic, flanked, geminate, geminated, handed,
   identical, lateral, many-sided, matched, multilateral, one-sided,
   polyhedral, quadrilateral, second, secondary, sided, tetrahedral,
   three-sided, trihedral, trilateral, triquetrous, twain, twin,
   twinned, two, two-faced, two-level, two-ply, two-sided, two-story,
   twofold, unilateral