Wait on answer (5)
I believe the answer is:
serve
I believe this clue is a double definition.
'wait on' is the first definition.
(thesaurus)
'answer' is the second definition.
(I've seen this before)
(Other definitions for serve that I've seen before include "Put the ball in play in 7 down" , "Open play at tennis" , "Assist" , "Be adequate; put ball in play" , "Put the ball in play on court" .)