A disfigurement hidden by the old lady's cosmetic (7)
I believe the answer is:
mascara
'cosmetic' is the definition.
(I know that mascara is a type of make-up)
'a disfigurement hidden by the old lady's' is the wordplay.
'disfigurement' becomes 'scar' (I've seen this before).
'hidden by' is an insertion indicator (the outside letters hide the inside ones).
'the old lady' becomes 'ma' (both can mean mother).
'a'+'scar'='ascar'
'ascar' inserted within 'ma' is 'MASCARA'.
(Other definitions for mascara that I've seen before include "facial cosmetic" , "Make-up for eyelashes" , "black application" , "that accentuates lashes" , "Make-up item" .)