Use on USA trip as feeling sick (8)
I believe the answer is:
nauseous
'feeling sick' is the definition.
(I've seen this before)
'use on usa trip' is the wordplay.
'trip' indicates an anagram.
'use'+'on'+'usa'='useonusa'
'useonusa' is an anagram of 'NAUSEOUS'.
'as' is the link.
(Other definitions for nauseous that I've seen before include "Afflicted with feeling of imminent sickness" , "Sick-making" , "Causing feeling of sickness or disgust" , "Sickening" , "Feeling sensation of imminent sickness" .)