Associate, partner (12)
I believe the answer is:
collaborator
I believe this is a double definition.
'associate' is the first definition.
(I know that collaborator is a type of associate)
'partner' is the second definition.
(I know that partner can be written as collaborator)
(Other definitions for collaborator that I've seen before include "Quisling" , "Partner" , "who takes part in jobshare?" , "Fellow worker" , "Fellow-worker" .)