A lot vs. Alot: 9 Grammatical Pitfalls
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- "to grasp, enclose" (see yard (n.1)). Sense of "accomplice" is first recorded 1952, American English, from meaning "group united in common cause" (1719).
cohort co·hort (kō'hôrt')
A defined population group followed prospectively in an epidemiological study.