"of or pertaining to the night, used or done at night," late 15c. (Caxton), from Old French nocturnal "nightly, nocturnal," or directly from Late Latin nocturnalis, from Latin nocturnus "belonging to the night," from nox (genitive noctis) "night," cognate with Old English neaht (see night) + -urnus, suffix forming adjectives of time. Related: Nocturnally. Nocturnal emission "involuntary ejaculation during sleep" is recorded by 1813.
c. 1300, "something seen in the imagination or in the supernatural," from Anglo-French visioun, Old French vision "presence, sight; view, look, appearance; dream, supernatural sight" (12c.), from Latin visionem (nominative visio) "act of seeing, sight, thing seen," noun of action from past participle stem of videre "to see," from PIE root *weid- "to see." The meaning "sense of sight" is first recorded late 15c. Meaning "statesman-like foresight, political sagacity" is attested from 1926.
c. 1200, innsihht, "sight with the 'eyes' of the mind, mental vision, understanding from within," from in (prep.) + sight (n.). But the meaning often seems to be felt as "sight into" (something else), and so the sense shifted to "penetrating understanding into character or hidden nature" (1580s). Similar formation in Dutch inzigt, German einsicht, Danish indsigt.