From Greek 'ideîn' (to see), from PIE *weid- — for Plato an eternal Form, not a passing thought; kin to 'video' and 'wisdom.'
A thought or suggestion as to a possible course of action; a concept or mental impression formed by the mind.
From Latin idea, from Greek idea (form, pattern, archetype), from idein (to see), the aorist infinitive of horan (to see). Idein derives from the PIE root *weyd- (to see, to know), one of the most philosophically significant roots in Indo-European. From *weyd- came Latin vidēre (to see — hence English video, vision, visit, evident, provide, supervise, revise), Latin vīsus (sight), Sanskrit veda (knowledge — the Vedas are literally books of knowledge), Old English witan (to know — hence English wit, witness, wisdom), Old English wīse (
The PIE root *weid- (to see) produced both Greek 'idea' and Latin 'video' (I see), Sanskrit 'Veda' (sacred knowledge), and English 'wit,' 'wise,' 'wisdom,' and 'witness.' Across all these languages, 'seeing' and 'knowing' are the same concept — an idea is literally something you have 'seen' with the mind's eye.