Hideous-sounding citrus fruit (4)
I believe the answer is:
ugli
'citrus fruit' is the definition.
(I know that Ugli is a type of citrus fruit)
'hideous-sounding' is the wordplay.
'hideous' becomes 'ugly' (similar in meaning).
'sounding' indicates a 'sounds like' (homophone) clue.
'ugly' sounds like 'UGLI'.
(Other definitions for ugli that I've seen before include "Black/violet element" , "West Indian citrus fruit" , "Jamaican form of 6" , "Cross between Seville orange, grapefruit and tangerine" , "Citrus fruit cross (which sounds offensive!)" .)