Why does "savior" have an "i"?

Savor or saver (cf. lifesaver) both seem more plausible. Why is there an i before the -or ending?

Solution 1:

According to the Oxford English Dictionary, the history of the word's form is as follows:

Forms: ME sauveur, ME sauveour, ME saveour(e, ME sauveor, saveor, saviur, savour, safeoure, Sc. safare, saweoure, ME, 15 sauvour, savioure, ME–15 savyour(e, ME savyowur, ME–15 savyor, 15 salveour, salviour, Sc. salvior, salweour, ME, 15–17 (18 chiefly U.S.) savior, ME– saviour.(Show Less)

Etymology: < Old French sauveour (modern French sauveur) = Provençal salvador, Spanish salvador, Portuguese salvador, Italian salvatore < late Latin salvātōr-em, agent-n. < salvāre to save v.

The English form has changed (including being savour for a time), but from the history you can see that the vast majority of forms have had i or e or even y to maintain the pronunciation. This is because the word comes from the Old French sauveour, so English spelling has maintained much of its root.