Osric once (I think) displays vanity (7)
I believe the answer is:
conceit
'vanity' is the definition.
('conceit' can be a synonym of 'vanity')
'osric once i think displays' is the wordplay.
'displays' says the answer is hidden in the clue.
'CONCEIT' is hidden within 'osric once i think'.
(Other definitions for conceit that I've seen before include "Excessive pride; fancy" , "Vanity; fanciful notion" , "antique ornament" , "Fancy; vanity" , "Excessive self-esteem" .)