Oral, a.
Etymology: [L. os, oris, the mouth, akin to Skr. as. Cf. Adore, Orison, Usher.]
1. Uttered by the mouth, or in words; spoken, not written; verbal; as, oral traditions; oral testimony; oral law.
2. Of or pertaining to the mouth; surrounding or lining the mouth; as, oral cilia or cirri.
Shades of meaning
Fernald has no entry of its own for oral; he lists it under verbal.
Where he writes about it:
Oral (L. os, the mouth) signifies uttered through the mouth or (in common phrase) by word of mouth; verbal (L. verbum, a word) signifies of, pertaining to, or connected with words, especially with words as distinguished from the ideas they convey; vocal (L. vox, the voice) signifies of or pertaining to the voice, uttered or modulated by the voice, and especially uttered with or sounding with full, resonant voice; literal (L. litera, a letter) signifies consisting of or expressed by letters, or according to the letter, in the broader sense of the exact meaning or requirement of the words used; what is called "the letter of the law" is its literal meaning without going behind what is expressed by the letters on the page. — from verbal
Thus oral applies to that which is given by spoken words in distinction from that which is written or printed; as, oral tradition; an oral examination. — from verbal
By this rule we should in strictness speak of an oral contract or an oral message, but verbal contract and verbal message, as indicating that which is by spoken rather than by written words, have become so fixed in the language that they can probably never be changed; this usage is also in line with other idioms of the language; as, "I give you my word," "a true man's word is as good as his bond," "by word of mouth," etc. — from verbal
A verbal translation may be oral or written, so that it is word for word; a literal translation follows the construction and idiom of the original as well as the words; a literal translation is more than one that is merely verbal; both verbal and literal are opposed to free. — from verbal
Vocal has primary reference to the human voice; as, vocal sounds, vocal music; vocal may be applied within certain limits to inarticulate sounds given forth by other animals than man; as, the woods were vocal with the songs of birds; oral is never so applied, but is limited to articulate utterance regarded as having a definite meaning; as, an oral statement. — from verbal