Use of this word spans several disciplines.

Problem:
“Cohort” has multiple meanings.

Explanation:
Demographers, epidemiologists, and market researchers use the noun “cohort” to mean a group of individuals with a common statistical factor (e.g., age).

Historians use “cohort” to refer to an infantry company in a Roman legion.

However, the two most common uses of “cohort” are a group of people and an individual associate.

Talk about contradictory definitions!

So “cohort” is both a singular noun and a plural noun.

Solution:
Be careful with how you use the noun “cohort”; otherwise, your readers may misunderstand you or may challenge how you use it.