early 14c., "body of men associated by common interest," from Old French fraternité (12c.), from Latin fraternitatem (nominative fraternitas) "brotherhood," from fraternus "brotherly," from frater "brother," from PIE *bhrater "brother" (see brother). Meaning "state or condition of being as brothers" is from late 15c. College Greek-letter organization sense is from 1777, first in reference to Phi Beta Kappa.