Sicken (3)
'sicken' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ail that I've seen before include "Worry" , "Be unwell, suffer" , "Be the worse for wear" , "upset" , "Trouble, afflict; be sickly" .)
'sicken' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for nauseate that I've seen before include "Sicken" , "Make to feel imminent sickness, turn stomach" , "Cause sick or disgusted feeling" , "Eaten in USA - would make you feel sick" , "Make (someone) sick" .)