(often + with) to work together or to work with somebody else on a common project or with a common aim
(often + with) to cooperate with an enemy of one's country
collaboration /-ʹraysh(ə)n/ noun
collaborative /-rətiv/ adj
collaboratively /-rətivli/ adv
collaborator noun
[late Latin collaboratus, past part. of collaborare to labour together, from co- + Latin laborare to work]