WordNet (r) 3.0 (2006):

midsection
    n 1: the middle area of the human torso (usually in front);
         "young American women believe that a bare midriff is
         fashionable" [syn: middle, midriff, midsection]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "midsection":
   barrier, brattice, buffer, buffer state, bulkhead, bumper, cloison,
   collision mat, cushion, diaphragm, dissepiment, dividing line,
   dividing wall, division, fender, interseptum, mat, midriff, pad,
   panel, paries, partition, party wall, property line, separation,
   septulum, septum, shock pad, wall