What is the X in X-mas?
early 12c., from Anglo-French cuncile, from Old North French concilie (Old French concile, 12c.) "assembly; council meeting; body of counsellors," from Latin concilium "group of people, meeting," from com- "together" (see com-) + calare "to call" (see claim (v.)). Tendency to confuse it in form and meaning with counsel has been consistent since 16c.
spoken of counsellors who sat in public trials with the governor of a province (Acts 25:12). The Jewish councils were the Sanhedrim, or supreme council of the nation, which had subordinate to it smaller tribunals (the "judgment," perhaps, in Matt. 5:21, 22) in the cities of Palestine (Matt. 10:17; Mark 13:9). In the time of Christ the functions of the Sanhedrim were limited (John 16:2; 2 Cor. 11:24). In Ps. 68:27 the word "council" means simply a company of persons. (R.V. marg., "company.") In ecclesiastical history the word is used to denote an assembly of pastors or bishops for the discussion and regulation of church affairs. The first of these councils was that of the apostles and elders at Jerusalem, of which we have a detailed account in Acts 15.
in the Christian Church, a meeting of bishops and other leaders to consider and rule on questions of doctrine, administration, discipline, and other matters. An ecumenical or general council is a meeting of bishops of the whole church; local councils representing such areas as provinces or patriarchates are often called synods. According to Roman Catholic doctrine, a council is not ecumenical unless it has been called by the pope, and its decrees are not binding until they have been promulgated by the pope. Decrees so promulgated have the highest authority in the Roman Catholic Church.