Entreat to be good (3)
I believe the answer is:
beg
'entreat' is the definition.
(I've seen this in another clue)
'be good' is the wordplay.
'good' becomes 'g' (abbreviation).
'be'+'g'='BEG'
'to' is the link.
(Other definitions for beg that I've seen before include "Ask humbly" , "Solicit charity" , "Plead or importune" , "Get by any means - . . ., borrow or steal" , "Ask for money, scrounge" .)