All 4 Uses

collaborate
in
Tamar, by Mal Peet
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Some of our people are collaborators; some are heroes.†
So, if he wanted to get to Banjo—and Tamar was fairly certain hewould—he'd have to be guided there by a relay of contacts and couriers, any one of whom could be a collaborator or Gestapo double agent.†
*
He had reminded his fellow countrymen—Dart had insisted on this bit—that volunteering to work for the Third Reich was a form of collaboration.†

collaboration = the act of working together
A Dutch collaborator called Slagter would translate.†

Definitions:

(1) (collaborate)
work together on a common enterprise or project

or more rarely and especially in the form collaborator: cooperate with the enemy as a traitor
(2) (meaning too rare to warrant focus)