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 as a son," from ad- "to" (see ad-) + filius "son" (see filial). Figurative sense of "adoption by a society, of branches" first recorded 1799 (the verb affiliate in a related sense is from 1761). Meaning "friendship, relationship, association" is from 1852.