affiliation (n.) Look up affiliation at Dictionary.com
1751, "adoption," from French affiliation, from Medieval Latin affiliationem (nominative affiliatio), noun of action from past participle stem of Latin affiliare "to adopt a son," from ad- "to" (see ad-) + filius "son" (see filial). Figurative sense of "adoption by a society, of branches" first recorded 1799 (affiliate in this sense is from 1761).