A blemish covered by old woman’s make-up (7)
I believe the answer is:
mascara
'make-up' is the definition.
(I've seen this before)
'a blemish covered by old woman's' is the wordplay.
'blemish' becomes 'scar' (scarring is a kind of blemishing).
'covered by' means one lot of letters goes inside another.
'old woman' becomes 'ma' (both can mean someone's mother).
'a'+'scar'='ascar'
'ascar' put inside 'ma' is 'MASCARA'.
(Other definitions for mascara that I've seen before include "Maracas (anag.)" , "for application of lashes" , "Type of make-up" , "Eyelash darkener" , "that accentuates lashes" .)