Groom fronting old jazz band (5)
I believe the answer is:
combo
'jazz band' is the definition.
('combo' can be a synonym of 'jazz band')
'groom fronting old' is the wordplay.
'groom' becomes 'comb' (combing is a kind of grooming).
'fronting' suggests taking the first letters (I've seen 'front' mean this).
The initial letter of 'old' is 'o'.
'comb'+'o'='COMBO'
(Other definitions for combo that I've seen before include "Small pop group" , "Small jazz group" , "Small (jazz or rock) band" , "group of players" , "Music group" .)