Ill; nauseous (4)
I believe the answer is:
sick
I believe this clue is a double definition.
'ill' is the first definition.
(I know that ill can be written as sick)
'nauseous' is the second definition.
(I know that nauseous can be written as sick)
(Other definitions for sick that I've seen before include "Bad" , "not good" , "Poorly" , "Ill; nauseous" , "Ill; perverted" .)