Acknowledgement that may be jolly? (5)
I believe the answer is:
roger
'jolly?' is the definition.
Both the definition and answer are verbs in their base form.
Perhaps they are linked in a way I don't understand?
I don't understand the remainder of the clue.
(Other definitions for roger that I've seen before include "Boy's name - message understood" , "Received (in radio comms)" , "Sir - de Coverley, English country dance" , "... guy" , "Radio acknowledgment" .)