Mother hides a blemish with make-up (7)
I believe the answer is:
mascara
'make-up' is the definition.
(I've seen this before)
'mother hides a blemish' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'hides' means one lot of letters goes inside another.
'blemish' becomes 'scar' (scarring is a kind of blemishing).
'a'+'scar'='ascar'
'ma' placed around 'ascar' is 'MASCARA'.
'with' acts as a link.
(Other definitions for mascara that I've seen before include "Eyelash make-up" , "Maracas (anag.)" , "Make-up for eyelashes" , "Make-up item" , "facial cosmetic" .)