Severe wife burning trousers (9)
I believe the answer is:
swingeing
'severe' is the definition.
(I've seen this before)
'wife burning trousers' is the wordplay.
'wife' becomes 'w' (abbreviation).
'burning' becomes 'singeing' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'trousers' is an insertion indicator (trouser can mean to steal or take).
'w' put within 'singeing' is 'SWINGEING'.
Can you help me to learn more?
(Other definitions for swingeing that I've seen before include "Painfully severe (cuts, fine)" , "Huge" , "Extreme" , "Thumping" .)