Mother with blemish getting a cosmetic (7)
I believe the answer is:
mascara
'cosmetic' is the definition.
(I know that mascara is a type of make-up)
'mother with blemish getting a' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'with' means one lot of letters go next to another.
'blemish' becomes 'scar' (scarring is a kind of blemishing).
'getting' says to put letters next to each other.
'ma'+'scar'+'a'='MASCARA'
(Other definitions for mascara that I've seen before include "Make-up for eyelashes" , "black application" , "Eyelash make-up" , "Maracas (anag.)" , "Cosmetic for darkening the eyelashes" .)