Mum's outfit, with antique flower (8)
I believe the answer is:
marigold
'flower' is the definition.
(marigold is a kind of flower)
'mum's outfit with antique' is the wordplay.
'mum' becomes 'ma' ('ma' can be a synonym of 'mum').
'outfit' becomes 'rig' ('rig' can be a synonym of 'outfit'**).
'with' says to put letters next to each other.
'antique' becomes 'old' ('old' can be similar in meaning to 'antique').
'ma'+'rig'+'old'='MARIGOLD'
(Other definitions for marigold that I've seen before include "The flower has a gold rim, oddly" , "Yellow or orange flower" , "Orange daisy" , "Flower - grim load (anag)" , "floral item" .)