late Middle English: from Old French cohorte, or from Latin cohors, cohort- 'yard, retinue'. Compare with court
The earliest sense of cohort is ‘a unit of men within the Roman army’. In the mid 20th century a new sense developed in the US, meaning ‘a companion or colleague’, as in young Jack arrived with three of his cohorts. Although this use is well established (it accounts for the majority of the citations for this word in the Oxford English Corpus), some people object to it on the grounds that cohort should only be used for groups of people, never for individuals.