http://www.californialaborlawattorney.com/implied-and-oral-c...

Contrary to common wisdom, an informal exchange of promises can still be binding and legally as valid as a written contract. A spoken contract is often called an "oral contract", not a "verbal contract." A verbal contract is simply a contract that uses words. All oral contracts and written contracts are verbal contracts. Contracts that are created without the use of words are called "non-verbal, non-oral contracts" or "a contract implied by the acts of the parties."

Since you're the one claiming "verbal" equals "oral", you're the one who's supposed to do the research. Wikipedia has a citation on that specific paragraph and there are lots of results in Google. Do your homework before your claims.

But anyways, "verbum, verbi" means "word" in Latin while "os, oris" means "mouth". That should be a clue.