h₂weyd-
“to see, to know (having seen)”see/know
PIE root meaning to see or to know from having seen. Source of Sanskrit veda, Latin vidēre, English "wit" and "vision."
Discussion
The root *h₂weyd- ("to see, to know from having seen") is one of the most important PIE verbal roots, treated in LIV² (s.v. *weyd-; some reconstructions include the laryngeal) and Pokorny (IEW 1125–1127). The connection between seeing and knowing is fundamental to PIE epistemology: knowledge was conceived as the result of having seen.
The perfect *wóyd-h₂e ("I have seen" → "I know") is independently preserved in Sanskrit véda ("I know"), Greek oîda (οἶδα, "I know"), Latin vīdī ("I saw", reinterpreted as a simple past), and Gothic wait ("I know"). This is one of the most celebrated correspondences in comparative linguistics and was among the evidence used by early Indo-Europeanists to establish the genetic relationship.
Latin vidēre ("to see") yields an enormous English vocabulary: vision, visible, visit, visor, evident, provide, provident, prudent (from prōvidēns), video, view (via Old French), and advice (from ad-vīsum). The noun idea itself comes from Greek idéā (ἰδέα, "form, appearance"), from the aorist stem *wid- of the same root.
Greek eîdos (εἶδος, "form, shape, kind") continues the o-grade and gives English -oid ("having the form of") in compounds like asteroid and android. Historíā (ἱστορία, "inquiry, knowledge from investigation") derives from hístōr ("one who knows, judge"), from *wid-tor, giving English history and story.
In Germanic, Grimm's Law gives *w- > *w-, *d > *t: Old English witan ("to know"), wīs ("wise"), and wit preserve the root. German wissen ("to know") and weise ("wise") are cognates. The English guide (via Old French, from Germanic *wītan) extends the sense to "one who knows the way."
Sanskrit vidyā́ ("knowledge") gives Veda (the sacred knowledge texts), one of the root's most culturally significant descendants.
Notes
Source of Latin "vidēre" (to see), English "wit", Sanskrit "véda". Vision → knowledge.