Mother returns our love (5)
I believe the answer is:
amour
'love' is the definition.
('love' in French)
'mother returns our' is the wordplay.
'mother' becomes 'ma' (ma can mean mother).
'returns' shows that the letters should be reversed in order.
'ma' written backwards gives 'am'.
'am'+'our'='AMOUR'
(Other definitions for amour that I've seen before include "Illicit love" , "20 [AFFAIR]" , "Romantic affair" , "Love-affair" , "A secret love affair in France" .)