The Collaborative International Dictionary of English v.0.48:

Bisect \Bi*sect"\, v. t. [imp. & p. p. Bisected; p. pr. & vb.
   n. Bisecting.] [L. bis twice + secare, sectum, to cut.]
   1. To cut or divide into two parts.
      [1913 Webster]

   2. (Geom.) To divide into two equal parts.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bisect
    v 1: cut in half or cut in two; "bisect a line"

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "bisect":
   amputate, average, ax, bifurcate, branch, butcher, by two, carve,
   chop, cleave, cut, cut away, cut in two, cut off, dichotomize,
   dimidiate, dissever, divide, double, excise, fission, fissure,
   fold, fork, gash, hack, halve, hew, in half, incise, jigsaw, lance,
   middle, pare, prune, ramify, rend, rive, saw, scissor, sever,
   slash, slice, slit, snip, split, split in two, subdivide, sunder,
   tear, transect, whittle