Female (Heather)’s brief affair (5)
I believe the answer is:
fling
'brief affair' is the definition.
(I've seen this before)
'female heather's' is the wordplay.
'female' becomes 'f' (abbreviation).
'heather' becomes 'ling' ('ling' can be a synonym of 'heather').
'f'+'ling'='FLING'
(Other definitions for fling that I've seen before include "Toss" , "Launch or propel" , "Highland dance - spell of way-out behaviour" , "Spell of indulgence" , "Hurl" .)