witness
Before "witness" meant a person, it meant the knowing itself. Old English witnes was an abstract noun — wit (knowledge) + -nes — for the state of having seen. The pivot to "the one who saw" came in Middle English. Underneath: PIE *weid-, "to see" — the same root as Latin video, Greek oida ("I have seen, therefore I know"), Sanskrit veda.
A witness today is a person — the one who saw the thing happen, summoned to testify. The word didn't start as a person. Witnes in Old English was an abstract noun: wit (knowledge) plus -nes, the suffix that gives darkness from dark, kindness from kind. Witness was knowing-ness — the state of having seen, the thing you carried in your head once you'd been there. To bear witness was to bear the knowing. The word for the role was the word for the cargo.
Underneath, the eye and the knowing collapse into one root. PIE *weid- meant "to see" — and gave Old English witan, "to know." The branches preserve the equation. Latin video, "I see." Greek oida, "I know" — formally the perfect tense of idein, "to see": I have seen, therefore I know. Sanskrit veda, knowledge. Across the Indo-European world, knowledge is the residue of having looked. Witness is what stays.
- wit — what you have when you've seen — the noun the word was built from
- wise — one who knows; the Germanic branch of the seeing-knowing equation
- view, vision, video — the Latin branch — the seeing itself, before the knowing
- idea — Greek; from idein, "to see." Form, derived from sight.
- guide — one who sees the way for others
- veda — knowledge, in the Indian branch
- evident — fully seen; standing out to be seen
- déjà vu — already-seen — the seeing recurring before the explanation