Pressure provided by affair is trivial (8)
I believe the answer is:
piffling
'trivial' is the definition.
(thesaurus)
'pressure provided by affair' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'provided' becomes 'if'.
'by' says to put letters next to each other.
'affair' becomes 'fling' (I have seen 'Brief affair' mean 'fling' so perhaps 'affair' could also mean 'fling').
'p'+'if'+'fling'='PIFFLING'
'is' is the link.
(Other definitions for piffling that I've seen before include "Minor" , "Nugatory" , "Mickey Mouse" , "Informally trivial or worthless" , "Of no importance at all" .)