Vain yet possibly showing innocence (7)
I believe the answer is:
naivety
'innocence' is the definition.
(naive can mean innocent or gullible)
'vain yet possibly' is the wordplay.
'possibly' is an anagram indicator.
'vain'+'yet'='vainyet'
'vainyet' with letters rearranged gives 'NAIVETY'.
'showing' acts as a link.
(Other definitions for naivety that I've seen before include "Navy tie shows lack of sophistication" , "artlessness" , "credulousness" , "Quality of impractical innocence" , "Inexperience" .)