New ideas in reserve (5)
I believe the answer is:
aside
'in reserve' is the definition.
(synonyms)
'new ideas' is the wordplay.
'new' indicates anagramming the letters.
'ideas' with letters rearranged gives 'ASIDE'.
(Other definitions for aside that I've seen before include "Remark by an actor, directly to audience say" , "(Pushed) out of the way" , "Line spoken to theatre audience" , "Apart; incidental remark" , "Out of other people's hearing" .)