Send out clock put back (4)
I believe the answer is:
emit
'send out' is the definition.
(I've seen this before)
'clock put back' is the wordplay.
'clock' becomes 'time' (synonyms).
'put back' shows that the letters should be reversed in order.
'time' written backwards gives 'EMIT'.
(Other definitions for emit that I've seen before include "Come out!" , "shed" , "Expel" , "Broadcast" , "Send out in time" .)