cueyoudaoicibaDictYouDict[cue 词源字典]
cue: Cue has several meanings in English, and it is not clear whether they can all be considered to be the same word. In the case of ‘pigtail’ and ‘billiard stick’, both of which appeared in the 18th century, cue is clearly just a variant spelling of queue, but although cue ‘actor’s prompt’ [16] has been referred by some to the same source (on the grounds that it represents the ‘tail’ – from French queue ‘tail’ – of the previous actor’s speech) there is no direct evidence for this.

Another suggestion is that it represents qu, an abbreviation of Latin quando ‘when’ which was written in actor’s scripts to remind them when to come in.
=> queue[cue etymology, cue origin, 英语词源]
cue (v.)youdaoicibaDictYouDict
1928, from cue (n.1). Related: Cued, cueing.
cue (n.1)youdaoicibaDictYouDict
"stage direction," 1550s, from Q, which was used 16c., 17c. in stage plays to indicate actors' entrances, probably as an abbreviation of Latin quando "when" (see quandary) or a similar Latin adverb. Shakespeare's printed texts have it as both Q and cue.
cue (n.2)youdaoicibaDictYouDict
"billiard stick," 1749, variant of queue (n.). Cue ball first recorded 1881.