Sound of a watch (4)
I believe the answer is:
tick
'sound of a watch' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tick that I've seen before include "Arrangement for deferred payment" , "Moment - parasitic arachnid" , "Credit; clock sound" , "Parasite - mark of approval" , "Credit; insect" .)