collaborator

noun

A person who works jointly on an activity or project; an associate.

SYNONYMS

allyassistantassociatebetrayerco-partnerco-workercollaborationistcolleaguecolluderconfederateconspiratordefectordouble agentfellow workerfifth columnistfraternizerhelperinformeroppopartnerquislingrenegadeteammatetraitorturncoat