"fasten, join, attach," 1530s, from Medieval Latin affixare, frequentative of Latin affigere (past participle affixus) "fasten to, attach," from ad "to" (see ad-) + figere "to fasten" (from PIE root *dheigw- "to stick, fix").
According to OED first used by Scottish writers and thus perhaps the immediate source was French affixer, a temporarily re-Latinized spelling of Old French afichier (Modern French afficher), from a Medieval Latin variant of the Latin verb. The older form in English was affitch (Middle English afficchen, late 14c.), from Old French afichier. Related: Affixed; affixt; affixing.
"that which is joined or attached," 1610s, from affix (v.) or from French affixe, noun use of the adjective from the verb in French. Related: Affixal.