Radiotelephony response (5)
I believe the answer is:
wilco
'radiotelephony response' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for wilco that I've seen before include "Roger might be followed by this" , "expression of agreement" , "Term of agreement (in radio communication)" , "Radio comms expression of compliance" , "it indicated acquiescence" .)