Cause to feel sick (8)
I believe the answer is:
nauseate
'cause to feel sick' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nauseate that I've seen before include "Cause to feel sick" , "Sicken" , "Make (someone) sick" , "Eaten in USA - would make you feel sick" , "Cause sick or disgusted feeling" .)