Mature returns collected by curious bunch (7)
I believe the answer is:
nosegay
'bunch' is the definition.
(I have seen 'Bunch of flowers ' mean 'nosegay' so perhaps 'bunch' could also mean 'nosegay')
'mature returns collected by curious' is the wordplay.
'mature' becomes 'age' ('age' can be a synonym of 'mature').
'returns' is a reversal indicator.
'collected by' means one lot of letters goes inside another.
'curious' becomes 'nosy' ('nosy' can be similar in meaning to 'curious').
'age' written backwards gives 'ega'.
'ega' put inside 'nosy' is 'NOSEGAY'.
(Other definitions for nosegay that I've seen before include "pick of the bunch" , "Small scented bunch of flowers" , "Fragrant posy" , "Gone, say (anag)" , "Small bouquet" .)