Boyd’s Bible Dictionary:

(learner). Follower of Christ (Matt. 10:24); of John (Matt. 9:14). Applied specially to the twelve (Matt. 10:1; 11:1; 20:17).

Concise Bible Dictionary:

This word signifies strictly “a learner” or “pupil.” The Pharisees had such, whom they taught to fast (Matt. 22:16; Mark 2:18). John the Baptist had disciples, who likewise fasted (Matt. 9:14; Luke 5:33; John 3:25). The Lord Jesus had His disciples: the apostles whom He chose to be with Him are called His “twelve disciples” (Matt. 11:1); but in other places the term is applied to all who followed the Lord, many of whom “went back and walked no more with him” (John 6:60-66). When great multitudes followed the Lord, He turned to them and bade them count the cost of really following Him. Such an one must hate (in comparison with Christ) all his natural relations and his own life also. He must take up his cross and follow Christ, and he must forsake all that he had, or he could not be His disciple (Luke 14:26-33). On another occasion Jesus said to the Jews that believed on Him, “If ye abide in my word, ye are truly my disciples” (John 8:31). It was true association in heart with a rejected Christ (Matt. 10:24-25; John 15:8).

From Manners and Customs of the Bible:

Luke 2:46. They found him in the temple, sitting in the midst of the doctors, both hearing them, and asking them questions.
There were several places within the Temple area where doctors of the law met their disciples. One of these places was in the cloisters described in the note on Matthew 24:1 (#704). Another was in the synagogue which was in the Temple enclosure. After service the doctors admitted any who wished to converse with them on matters pertaining to the law. There were also other places resorted to for a similar purpose; and Lightfoot declares that it was not impossible for Jesus to have been in the great Sanhedrim itself.
There is no reason to suppose that in the conversation which Jesus held with these learned men there was anything like controversy. He simply followed the custom of the time, which allowed anyone who chose to question the doctors on any points on which they desired information.

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