Passionate old woman about to be involved in affair (7)
I believe the answer is:
flaming
'passionate' is the definition.
(I've seen this before)
'old woman about to be involved in affair' is the wordplay.
'old woman' becomes 'ma' (I've seen this in other clues).
'about' says the letters should be written backwards.
'to be involved in' means one lot of letters goes inside another.
'affair' becomes 'fling' (I have seen 'Brief affair' mean 'fling' so perhaps 'affair' could also mean 'fling').
'ma' reversed gives 'am'.
'am' put within 'fling' is 'FLAMING'.
(Other definitions for flaming that I've seen before include "Passionate" , "Brightly coloured" , "Ardent" , "Fiery" , "Burning fiercely" .)