A cohort may mean

1. a sub-division of the Roman infantry. Originally it was a sub-unit of a Roman legion, consisting of 600 men, itself divided in 6 centurias of 100 men commanded each by a centurion. In the Imperial Roman auxiliary forces, there were individual cohorts of 500 (quingenaria), and 1000 (miliaria), as well as mixed infantry and cavalry units (cohors equitata) that existed in parallel.
2. an age group in statistics, see cohort (statistics).
3. a concept in computer science.
4. in biology, cohort is a term for a group of allied orders or families of plants or animals.
5. a supporter (American English usage from around 1950).