mid-13c., counseiler, "one who gives counsel or advice, a confidante," from Old French conseillier "counselor, adviser" (Modern French conseiller), from Latin consilator, agent noun from consiliare, from consilium (see counsel (v.)).
Also sometimes counsellor, but the double -l- is unetymological and perhaps is modeled on chancellor. Meaning "one who gives professional legal advice, a counseling lawyer," is from 1530s. Psychological sense (as in marriage counselor, is from 1940).
c. 1200, "advice or instruction given;" c. 1300, "mutual advising or interchange of opinions, consultation," from Old French counseil "advice, counsel; deliberation, thought" (10c.), from Latin consilium "plan, opinion," from assimilated form of com "with, together" (see con-) + root of calare "to announce, summon" (from PIE root *kele- (2) "to shout"). As a synonym for "lawyer, one who gives legal counsel," attested late 14c.
early 15c., dissuasioun, "advice or exhortation in opposition to something," from Old French dissuasion (14c.) and directly from Latin dissuasionem (nominative dissuasio) "an advice to the contrary," noun of action from past-participle stem of dissuadere "to advise against, oppose by argument," from dis- "off, against" (see dis-) + suadere "to urge, incite, promote, advise, persuade," literally "recommend as good" (related to suavis "sweet"), from PIE root *swād- "sweet, pleasant" (see sweet (adj.)).
also counselling, early 14c., "the giving or taking of counsel," verbal noun from counsel (v.). Meaning "the giving of professional advice on social or psychological problems" is attested by 1928.