An anthropological term referring to different sects of people, oftentimes unrelated by blood, cohabiting and copopulating the same society.  That is to say, clans banding together and actually getting along.  Say it isn’t so, Pellinore.  Oh, but it is.  Or was.  Phratry implies more than two distinct clans grouping together for common cause, or common food more likely.  Say it aloud — can you hear “fraterie” — yes, shares the same root as fraternity (from the Greek  φρατρί, the word for “clansman”).  Huzzah for etymology and the OED.