Laugh at last group ornament (7)
I believe the answer is:
hatband
'ornament' is the definition.
(hatband is a kind of ornament)
'laugh at last group' is the wordplay.
'laugh' becomes 'ha'.
'last' indicates one should take the final letters.
'group' becomes 'band' (band can mean a group of people).
The last letter of 'at' is 't'.
'ha'+'t'+'band'='HATBAND'
(Other definitions for hatband that I've seen before include "Part of headgear" , "Bowler may have one" , "Headgear decoration" .)