Fruit grew to be fashionable (7)
I believe the answer is:
rosehip
'fruit' is the definition.
(I've seen this before)
'grew to be fashionable' is the wordplay.
'grew' becomes 'rose' (I've seen this before).
'to be fashionable' becomes 'hip' (I've seen this before).
'rose'+'hip'='ROSEHIP'
(Other definitions for rosehip that I've seen before include "Hedgerow or garden fruit" , "Fruit of the briar" , "Wayside fruit" , "Red fruit" , "Fruit of a popular flower" .)