Open to entertaining vicar in retirement (5)
I believe the answer is:
overt
'open' is the definition.
(associated in meaning)
'to entertaining vicar in retirement' is the wordplay.
'entertaining' indicates putting letters inside (inviting in, as for dinner).
'vicar' becomes 'rev' (short for reverend).
'in retirement' says the letters should be written in reverse (retire can mean to go back or backwards).
'to' going around 'rev' is 'trevo'.
'trevo' written backwards gives 'OVERT'.
(Other definitions for overt that I've seen before include "Voter (anag.)" , "Open and observable" , "Conspicuous" , "Openly displayed" , "Patent, evident" .)