councilor n.

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).

"assembly of persons for consultation, deliberation or advice," early 12c., originally in the Church sense, "assembly of prelates and theologians to regulate doctrine and discipline," from Anglo-French cuncile, from Old North French concilie (Old French concile, 12c.) "assembly; council meeting; body of counsellors," from Latin concilium "a meeting, a gathering of people," from PIE *kal-yo-, suffixed form of root *kele- (2) "to shout." The notion is of a calling together. The tendency to confuse it in form and meaning with counsel has been consistent since 16c.

see councilor.