The use in sense cohort (3) arises from a misunderstanding of the plural form cohorts as meaning a group of which each member is a cohort, whereas a cohort is a group and cohorts are several groups. This misunderstanding is reinforced by confusion of the first syllable co- with words such as co-author and co-star, as if the spelling might be co-hort, a fellow hort (whatever that is). This meaning is creeping into British English: his chief cohort was an Englishman. There are much better alternatives: for example supporter, collaborator, henchman, and associate, as well as the two words given in the definition above