late 13c., auys "opinion," from Old French avis "opinion, view, judgment, idea" (13c.), from phrase ço m'est à vis "it seems to me," or from Vulgar Latin *mi est visum "in my view," ultimately from Latin visum, neuter past participle of videre "to see" (from PIE root *weid- "to see"). Meaning "opinion offered as worthy to be followed, counsel" is from late 14c.

The unetymological -d- (on model of Latin words in ad-) was inserted occasionally in French by scribes 14c.-16c. and was made regular in English 15c. by Caxton. Substitution of -c- for -s- is 18c., to preserve the breath sound and to distinguish from advise. Early Modern English tended to alternate -ce and -se endings in otherwise confusable noun-verb pairs, using -se for the verb and -ce for the noun: devise/device, peace/appease, practice/practise, license/licence, prophecy/prophesy.

1640s, ""prudent, expedient, proper to be advised," from advise (v.) + -able (q.v.). It also can mean "open to advice" (1660s), but this is rare.

1610s, "one who gives advice," agent noun from advise (v.). The meaning "faculty assigned to mentor students" is from 1887. The meaning "military person sent to help a government or army in a foreign country" is recorded from 1915. Alternative form, Latinate advisor, is perhaps a back-formation from advisory.

1778, "having the power to advise;" see advise + -ory. The noun meaning "weather warning" is from 1936, used by U.S. agencies, probably short for advisory bulletin.

obsolete form of advise. Related: Avisement.

1590s, from ill (adv.) + advised, past-participle adjective from advise (v.) in its original (but now obsolete) reflexive sense "take thought, consider." Related: Ill-advisedly.

late 14c., "not prudent or discrete; ill-considered;" from un- (1) + past participle of advise (v.). By 1851 as "not having received advice." Related: Unadvisedly.

Proto-Indo-European root meaning "to see."

It might form 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 might also be the source of: 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 widzieć "to see," wiedzieć "to know;" Russian videt' "to see," vest' "news," Old Russian vedat' "to know."