Dressing, group before getting on (9)
I believe the answer is:
bandaging
'dressing' is the definition.
(bandaging is a kind of dressing)
'group before getting on' is the wordplay.
'group' becomes 'band' (band is a kind of group**).
'before' means one lot of letters go next to another.
'getting on' becomes 'aging' (I've seen this before).
'band'+'aging'='BANDAGING'
(Other definitions for bandaging that I've seen before include "Providing cover" , "some first aid" , "holding together" .)