Covering a blemish with mother's make-up (7)
I believe the answer is:
mascara
'make-up' is the definition.
(I've seen this before)
'covering a blemish with mother's' is the wordplay.
'covering' is a charade indicator (letters next to each other) (on top of in down clue).
'blemish' becomes 'scar' (scarring is a kind of blemishing**).
'with' says to put letters next to each other.
'mother' becomes 'ma' (ma is a kind of mother).
'scar' put after 'ma' is 'mascar'.
'a' put after 'mascar' is 'MASCARA'.
(Other definitions for mascara that I've seen before include "Cosmetic for darkening the eyelashes" , "black application" , "Makeup used to darken and thicken the eye lashes" , "could be found in handbag, perhaps" , "Type of make-up" .)