Cohort

Cohort: In a clinical study, a well-defined group of subjects or patients who have had a common experience or exposure and are then followed up for the incidence of new diseases or events, as in a cohort study.

In Rome, a "cohors" was one of ten divisions making up a Roman legion. The term came via French into English and came to refer to any body of troops and to any group of individuals with something in common.