Hard woman rejected cosmetic (5)
I believe the answer is:
henna
'cosmetic' is the definition.
(I've seen this before)
'hard woman rejected' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'woman' becomes 'anne' (I've seen this before).
'rejected' says the letters should be written in reverse.
'anne' reversed gives 'enna'.
'h'+'enna'='HENNA'
(Other definitions for henna that I've seen before include "Vegetable dye" , "Red-brown plant dye" , "Cosmetic plant dye" , "shock treatment" , "Type of dye" .)