Mongrel raves for fruit (8)
I believe the answer is:
currants
'mongrel raves for fruit' is the definition.
I can't tell whether this defines the answer.
'mongrel raves' is the wordplay.
'mongrel' becomes 'cur' (synonyms).
'raves' becomes 'rants' ('rant' can be a synonym of 'rave').
'cur'+'rants'='CURRANTS'
Can you help me to learn more?
(Other definitions for currants that I've seen before include "Small, dried, seedless raisins" , "Black or red berries" , "Dried fruit" , "Dried black grapes" , "Small dried fruits used in baking" .)