Nasty, unpleasant (4)
I believe the answer is:
icky
I believe this clue is a double definition.
'nasty' is the first definition.
(I've seen this before)
'unpleasant' is the second definition.
(icky can mean disgusting)
(Other definitions for icky that I've seen before include "Cloying -- repulsive" , "Repulsively sentimental" , "Sickly sweet" , "Distasteful - over-sentimental" , "horrid" .)