collaboration (n.)

1860, "act of working together, united labor" (especially in literature or scientific study), from French collaboration, noun of action from Latin collaborare "work with," from assimilated form of com "with" (see com-) + laborare "to work" (see labor (v.)).

In a bad sense, "traitorous cooperation with an occupying enemy," it is recorded from 1940; earliest references are to the Vichy Government of France. Collaborationist was used disparagingly in socialist jargon from 1922.