verbal

Where it comes from

Verbal ordinarily means relating to words, especially spoken rather than written words. Verbal came through French from Late Latin verbalis, meaning made of or concerned with words. Verbalis was formed from Latin verbum, word, which also supplied English verb. Because speech uses words, verbal developed the narrower sense spoken rather than written.

How the meaning developed

But the older, broader sense survived: writing can be verbal too, and a verbal translation can even mean word-for-word.

In use

“Verbal” means involving words. “Oral” specifically means spoken.
Which is unambiguously spoken: an oral warning or a verbal warning?

A verbal warning can mean a warning expressed in words and is often used for speech. But writing is made of words too.
Use “oral” when the spoken-not-written distinction matters.