Party possibly getting on. It's binding! (9)
I believe the answer is:
bandaging
'binding' is the definition.
(I know that binding can be written as bandaging)
'party possibly getting on' is the wordplay.
'party possibly' becomes 'band' (party is a kind of band).
'getting on' becomes 'aging' (I've seen this before).
'band'+'aging'='BANDAGING'
'it's' is the link.
(Other definitions for bandaging that I've seen before include "holding together" , "some first aid" , "Providing cover" .)