WordNet sense 1 (evidence that helps to solve a problem):

clew, clue

WordNet sense 2 (a stimulus that provides information about what to do):

discriminative stimulus

WordNet sense 3 (sports implement consisting of a tapering rod used to strike a cue ball in pool or billiards):

cue stick, pool cue, pool stick

WordNet sense 4 (assist (somebody acting or reciting) by suggesting the next words of something forgotten or imperfectly learned):

prompt, remind