Plain retired vicar dipping into Holy Writ (5)
I believe the answer is:
overt
'plain' is the definition.
(both can mean visible or obvious)
'retired vicar dipping into holy writ' is the wordplay.
'retired' says the letters should be written backwards.
'vicar' becomes 'rev' (reverend).
'dipping into' means one lot of letters goes inside another.
'holy writ' becomes 'OT' (Old Testament).
'rev' reversed gives 'ver'.
'ver' placed into 'ot' is 'OVERT'.
(Other definitions for overt that I've seen before include "totally visible" , "Plainly apparent" , "Open and undisguised" , "Patent, evident" , "Open, up front" .)