Lions' vanity (5)
I believe the answer is:
pride
This clue is a double definition.
'lions'' is the first definition.
(pride is the collective noun for a group of lions)
'vanity' is the second definition.
(I've seen this before)
(Other definitions for pride that I've seen before include "Arrogance - self-respect" , "cause of swelling?" , "Deadly sin (of lions?)" , "Novel by Jane Austen" , "big cats" .)