A cohort originally meant one of 10 divisions of a Roman legion (made up of 300 to 600 soldiers). The meaning was later expanded to mean any group of soldiers or warriors. It was further extended to describe any group of companions or supporters.
Today this noun also describes a group of person sharing a particular statistical or demographic characteristic.
The latest meaning of the word cohort is companion, associate, accomplice, or colleague. Using cohort to signify a single individual has upset some language scholars but this use is now very common.
Cohort entered English from the Middle French cohorte in the early 1400s. It is originally from the Latin cohort from cohors from co- (together) and hors (akin to hortus, which is the source of horticulture, the study of gardens).
A UNC football player was visiting a Yankee relative in Boston over the holidays. He went to a large party and met a pretty co-ed. He was attempting to start up a conversation with the line, "Where do you go to school?"
"Yale," she replied.
The UNC student took a big, deep breath and shouted, "WHERE DO YOU GO TO SCHOOL?"