1 An attribute of an object or event to which an organism responds, typical examples being the size or shape of a visual stimulus (1) to which a response may be conditioned.
2 A dimension or aspect of a proximal stimulus (3) on the basis of which an organism makes inferences about a distal stimulus (2), typical examples being the monocular and binocular depth cues on the basis of which depth perception occurs.
3 In research into memory, a stimulus that aids the recall of information not recalled spontaneously. See also acoustic cue (2), cued recall, priming (1), probe.
4 A signal to an actor or performer to begin performing, or more generally a hint about how to behave in a certain situation. vb.
5 To supply someone with a cue (3, 4). [Perhaps from French queue a tail, from Latin cauda a tail; in the 17th century written Q, standing for Latin quando when (the actor should begin)]