Appeared as a swelling in fruit (7)
I believe the answer is:
rosehip
'fruit' is the definition.
(fruit of a rose plant)
'appeared as a swelling in' is the wordplay.
I cannot quite see how this works, but
'appeared' could be 'rose' (rise can mean to appear or arrive) and 'rose' is present in the answer.
'in' could be 'hip' (both can mean fashionable) and 'hip' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rosehip that I've seen before include "Fruit of the brier" , "Part of plant" , "Hedgerow or garden fruit" , "Fruit of flower used for syrup" , "Berry for syrup" .)