The Spanish for “poster”, afiche, comes from the Latin figere, meaning, “to fasten”. From that same root, we get the English affix — and we can see that clearly, as the a‑f-ch of afiche maps clearly to the a‑f-x of affix.

More distantly, from the original Latin root figere, we get the English… fix. You can see the Latin root f‑g map to the English f‑x as well!