Hideous-sounding fruit (4)
I believe the answer is:
ugli
'fruit' is the definition.
(ugli fruit is a kind of fruit)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for ugli that I've seen before include "Jamaican form of 6" , "mixed fruit" , "Grapefruit/tangerine hybrid" , "Cross between Seville orange, grapefruit and tangerine" , "Mottled tangelo hybrid" .)