WordNet (r) 3.0 (2006):

bowels
    n 1: the center of the Earth

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "bowels":
   abdomen, anus, appendix, belly, blind gut, bottomless pit, brain,
   cecum, colon, core, deep space, deeps, depths, duodenum,
   endocardium, entrails, foregut, gaping depths, giblets, gizzard,
   gut, guts, heart, hell, hindgut, infernal pit, innards,
   inner mechanism, insides, interior, internals, intestine,
   intestines, inwards, jejunum, kidney, kishkes, large intestine,
   liver, liver and lights, lung, midgut, nether world, outer space,
   perineum, pump, pylorus, rectum, small intestine, spleen, stomach,
   ticker, tripes, underworld, unfathomed deeps, unknown depths,
   vermiform appendix, viscera, vitals, works



Easton's 1897 Bible Dictionary:

Bowels
   (Phil. 1:8; 2:1; Col. 3:12), compassionate feelings; R.V.,
   "tender mercies."