Rub mother's herb (7)
I believe the answer is:
massage
'rub' is the definition.
(I've seen this before)
'mother's herb' is the wordplay.
'mother's' becomes 'ma's' (Ma is another word for mother or mum).
'herb' becomes 'sage' (sage is a kind of herb).
'mas'+'sage'='MASSAGE'
(Other definitions for massage that I've seen before include "therapeutic treatment" , "Present favourably" , "See 10" , "Manipulate to get better results" , "Manipulate the muscles" .)