Same word as uncompassionate:

aloof, antipathetic, apathetic, aversive, callous, cold, cold-blooded, cool, cruel, disinterested, frigid, halfhearted, hard, harsh, heartless, icy, indifferent, insensitive, lukewarm, mean, nasty, obdurate, repellent, repugnant, stony, tough, uncaring, uncharitable, unconcerned, uncongenial, unemotional, unfeeling, unkind, unmoved, unpitying, unpleasant, unresponsive, unstirred, untouched