Opposite of "adorn" (3)
I believe the answer is:
mar
'opposite of adorn' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mar that I've seen before include "Damage; month (abbr.)" , "Disfigure" , "Oh dear!" , "'Impair, spoil (3)'" , "Spanish main?" .)