WordNet sense 1 (extremely painful):

agonizing, excruciating, harrowing, torturous, agonising, torturesome

WordNet sense 2 (causing physical or psychological pain):

painful

WordNet sense 3 (the deliberate, systematic, or wanton infliction of physical or mental suffering by one or more persons in an attempt to force another person to yield information or to make a confession or for any other reason):

torture