or

The root or comes from Latin ōs, ōris — 'the mouth.' (The genitive ōris is why the root surfaces as or- in English words, not os-.) It is a small but vivid root, because nearly every word it builds connects the physical mouth to the act of speaking — and from speaking, to prophesying.

The chain of meaning runs: mouth → what comes out of the mouth (speech) → formal speech → the person who speaks → the divine voice that speaks the future.

- oral: of the mouth — spoken rather than written (an oral exam, oral tradition)
- oration: a formal, ceremonial speech (or- + the action ending)
- orator: the person who delivers such a speech, a skilled public speaker
- oratory: the art of fine speaking — or, oddly, a small private chapel (a place for spoken prayer)
- oracle: literally 'the speaking place' — the mouth of the gods, where prophecies were uttered; also the priest or shrine that delivered them
- oracular: prophetic and mysterious, like an oracle's words

Two members reward a closer look. orifice is ōs/ōris (mouth) + fic- (a form of facere, 'to make') — literally 'a thing made into a mouth,' i.e. any opening, especially in the body. And orotund, describing a full, booming voice, comes from the Latin phrase ōre rotundō, 'with a round mouth' — Horace's image of clear, well-rounded speech, later soured into 'pompous.'

The big takeaway: when you see or- at the start of a word about speaking, speeches, or prophecy, it is the mouth-root at work. The mouth is where words are born, so the organ became the symbol of speech itself.

One caution worth flagging: not every or- word belongs here. Aphorism ('a short, wise saying') looks like it should — a wise thing from the mouth — but it actually comes from Greek aphorizein ('to mark off, define'), built on horos ('boundary'), with no connection to the Latin mouth-root. Same letters, unrelated source.