*weid- Proto-Indo-European root meaning "to see." It forms all or part of: advice; advise; belvedere; clairvoyant; deja vu; Druid; eidetic; eidolon; envy; evident; guide; guidon; guise; guy (n.1) "small rope, chain, wire;" Gwendolyn; Hades; history; idea; ideo-; idol; idyll; improvisation; improvise; interview; invidious; kaleidoscope; -oid; penguin; polyhistor; prevision; provide; providence; prudent; purvey; purview; review; revise; Rig Veda; story (n.1) "connected account or narration of some happening;" supervise; survey; twit; unwitting; Veda; vide; view; visa; visage; vision; visit; visor; vista; voyeur; wise (adj.) "learned, sagacious, cunning;" wise (n.) "way of proceeding, manner;" wisdom; wiseacre; wit (n.) "mental capacity;" wit (v.) "to know;" witenagemot; witting; wot. It is the hypothetical source of/evidence for its existence is provided by: Sanskrit veda "I know;" Avestan vaeda "I know;" Greek oida, Doric woida "I know," idein "to see;" Old Irish fis "vision," find "white," i.e. "clearly seen," fiuss "knowledge;" Welsh gwyn, Gaulish vindos, Breton gwenn "white;" Gothic, Old Swedish, Old English witan "to know;" Gothic weitan "to see;" English wise, German wissen "to know;" Lithuanian vysti "to see;" Bulgarian vidya "I see;" Polish widzie? "to see," wiedzie? "to know;" Russian videt' "to see," vest' "news," Old Russian vedat' "to know."

Sources:

• A Dictionary of Selected Synonyms in the Principal Indo-European Languages, University of Chicago (By: Carl Darling Buck) 1988.
• Etymological Dictionary of Latin and the other Italic Languages (By: Michiel de Vaan) 2008.
• The American Heritage Dictionary of Indo-European Roots (By: Calvert Watkins) 2000.
• Noun Declension in Indo-European (Sindhueuropaia Deklination Nomnes) By: Carlos Quiles.
• Online Etymology Dictionary (By: Douglas Harper)