Reticent about stray drink (6)
I believe the answer is:
sherry
'drink' is the definition.
(sherry is a kind of drink)
'reticent about stray' is the wordplay.
'reticent' becomes 'shy' (both can mean withdrawn or timid).
'about' is an insertion indicator.
'stray' becomes 'err' (to err is to stray or go wrong).
'shy' enclosing 'err' is 'SHERRY'.
(Other definitions for sherry that I've seen before include "Jerez tipple" , "Pre-dinner aperitif as from Jerez" , "Spanish drink" , "Alcohol for the trifle" , "Alcoholic appetiser associated with Jerez" .)