Has ideas inside privately (5)
I believe the answer is:
aside
'privately' is the definition.
(I've seen this before)
'has ideas inside' is the wordplay.
'inside' indicates a hidden word.
'ASIDE' is hidden within 'has ideas'.
(Other definitions for aside that I've seen before include "Words spoken apart in an undertone" , "kept in reserve" , "Out of other people's hearing" , "(Turn) off main path" , "Remark by an actor, directly to audience say" .)