Suspect vapour corrosion (8)
I believe the answer is:
mistrust
'suspect' is the definition.
(synonyms)
'vapour corrosion' is the wordplay.
'vapour' becomes 'mist' (water vapour).
'corrosion' becomes 'rust' (rust is a kind of corrosion).
'mist'+'rust'='MISTRUST'
(Other definitions for mistrust that I've seen before include "Lack of belief (in someone)" , "Regard with suspicion" , "Have no confidence in (someone)" , "Have doubts about" , "reservations" .)