(1.) In the natural and common sense (Matt. 1:2; Luke 3:1, 19). (2.) A near relation, a cousin (Gen. 13:8; 14:16; Matt. 12:46; John 7:3; Acts 1:14; Gal. 1:19). (3.) Simply a fellow-countryman (Matt. 5:47; Acts 3:22; Heb. 7:5). (4.) A disciple or follower (Matt. 25:40; Heb. 2:11, 12). (5.) One of the same faith (Amos 1:9; Acts 9:30; 11:29; 1 Cor. 5:11); whence the early disciples of our Lord were known to each other as brethren. (6.) A colleague in office (Ezra 3:2; 1 Cor. 1:1; 2 Cor. 1:1). (7.) A fellow-man (Gen. 9:5; 19:7; Matt. 5:22, 23, 24; 7:5; Heb. 2:17). (8.) One beloved or closely united with another in affection (2 Sam. 1:26; Acts 6:3; 1 Thess. 5:1). Brethren of Jesus (Matt. 1:25; 12:46, 50: Mark 3:31, 32; Gal. 1:19; 1 Cor. 9:5, etc.) were probably the younger children of Joseph and Mary. Some have supposed that they may have been the children of Joseph by a former marriage, and others that they were the children of Mary, the Virgin's sister, and wife of Cleophas. The first interpretation, however, is the most natural. The Hebrew word is used in various senses in the Old Testament, as, + Any kinsman, and not a mere brother; e.g. nephew, (Genesis 13:8; 14:16) husband, (Song of Solomon 4:9) + One of the same tribe. (2 Samuel 19:13) + Of the same people, (Exodus 2:11) or even of a cognate people. (Numbers 20:14) + An ally. (Amos 1:9) + Any friend, (Job 5:15) + One of the same office. (1 Kings 9:13) + A fellow man. (Leviticus 19:17) + Metaphorically of any similarity, as in (Job 30:19) The word adelphos has a similar range of meanings in the New Testament.
Brother