Impressive number invested in trophy (6)
I believe the answer is:
potent
'impressive' is the definition.
(thesaurus)
'number invested in trophy' is the wordplay.
'number' becomes 'ten' (ten is a kind of number).
'invested in' means one lot of letters goes inside another.
'trophy' becomes 'pot' (I've seen this before).
'ten' inserted into 'pot' is 'POTENT'.
(Other definitions for potent that I've seen before include "Intoxicating" , "Powerful, influential" , "Mighty" , "Powerful like strong drink" , "Top Ten (anag.)" .)