early 15c., "company of soldiers," from Middle French cohorte (14c.) and directly from Latin cohortem (nominative cohors) "enclosure," meaning extended to "infantry company" in Roman army (a tenth part of a legion) through notion of "enclosed group, retinue," from com- "with" (see co-) + root akin to hortus "garden," from PIE *ghr-ti-, from root *gher- (1) "to grasp, enclose" (see yard, n.1). Sense of "accomplice" is first recorded 1952, American English, from meaning "group united in common cause" (1719).