Lend beauty to part of a head ornament (5)
I believe the answer is:
adorn
'lend beauty to' is the definition.
(I've seen this in another clue)
'part of a head ornament' is the wordplay.
'part of' says the answer is hidden in the clue.
'ADORN' is hidden within 'head ornament'.
(Other definitions for adorn that I've seen before include "Beautify - decorate - enhance" , "Attire" , "Deck" , "Bedeck" , "Embellish, decorate" .)