(1 syl.). The tail of a sentence (French, queue), the catch-word which indicates when another actor is to speak; a hint; the state of a person's temper, as “So-and-so is in a good cue (or) bad cue.”
“When my cue comes, call me, and I will answer.” —Shakespeare: Midsummer Night's Dream, iv. 1.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894