af·fil·i·ate (-fl -t) v. af·fil·i·at·ed, af·fil·i·at·ing, af·fil·i·ates v. tr. 1. To adopt or accept as a member, subordinate associate, or branch: The HMO affiliated the clinics last year. 2. To associate (oneself) as a subordinate, subsidiary, employee, or member: affiliated herself with a new law firm. 3. To assign the origin of.