Trademarked citrus fruit (4)
I believe the answer is:
ugli
'trademarked citrus fruit' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ugli that I've seen before include "Hybrid fruit, sounds nasty" , "Trademark name for a hybrid citrus fruit" , "Cross between Seville orange, grapefruit and tangerine" , "Unappealing-sounding fruit?" , "Citrus fruit cross (which sounds offensive!)" .)