Elegant groom, last in vestry (6)
I believe the answer is:
dressy
'elegant' is the definition.
(I've seen this before)
'groom last in vestry' is the wordplay.
'groom' becomes 'dress' (dressing is a kind of grooming).
'last in' suggests the final letters.
The last letter of 'vestry' is 'y'.
'dress'+'y'='DRESSY'
(Other definitions for dressy that I've seen before include "Formal or elegant" , "(Of clothes) smart, formal" , "Smartly attired, wearing stylish clothes" , "Stylish with regard to clothes" , "Smartly clothed" .)