noun pl. fraternities -·ties

1. the state or quality of being brothers; fraternal relationship or spirit; brotherliness
2. a group of men (or, sometimes, men and women) joined together by common interests, for fellowship, etc.; specif., a Greek-letter college organization
3. a group of people with the same beliefs, interests, work, etc. the medical fraternity

Etymology: ME fraternite < OFr fraternité < L fraternitas < fraternus: see fraternal