Callousness rhymes with:
carelessness, helplessness, homelessness, hopelessness, joblessness, lawlessness, powerlessness, recklessness, restlessness, ruthlessness, weightlessness
Callousness sounds like:
calgene's, calkins, caulking, caulkins, chalking, clackamas, clashing, classing, clausing, clicking, cloaking, clocking, clogging, closeness, closing, closings, clucking, coalescence, coalescing, collegians, collisions