Heard signal for waiters to line up (5)
I believe the answer is:
queue
'line up' is the definition.
(synonyms)
'heard signal' is the wordplay.
'heard' shows a homophone (sound like).
'signal' becomes 'cue' (as in an actor's cue).
'cue' is a homophone of 'QUEUE'.
'for waiters to' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for queue that I've seen before include "orderly people?" , "Tailback" , "(Usually) orderly line" , "Pigtail; get in line" , "Form a line" .)