Answer bank privately (5)
I believe the answer is:
aside
'privately' is the definition.
(thesaurus)
'answer bank' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'bank' becomes 'side' ('side' can be a synonym of 'bank').
'a'+'side'='ASIDE'
(Other definitions for aside that I've seen before include "kept in reserve" , "Remark by an actor, directly to audience say" , "(Turn) off main path" , "Actor's remark for the audience alone" , "Words spoken apart in an undertone" .)