This word is used to describe men who were possessed by demons, as revealed in scripture. In the N.T. those 'possessed' by demons were certainly under the control of the demons, even to casting them into the fire and into the water.

It has been argued that the persons said to be possessed were really lunatics, who imagined they were possessed; and to meet that fancy the Lord spoke to the supposed spirit and told it to come out! But this is simply an effort to deny the power of Satan and his emissaries over man, and also God's power in the miracles. The Lord spoke of the casting out of demons when he was not speaking to those possessed. The demons also knew the Lord to be the Son of God, answered Him, asked permission to go into the herd of swine, and feared he had come to punish them before the time. Those who were lunatics are mentioned along with, and as different from, those possessed with demons. Matthew 4:24 . It is true that the father of a lad who was possessed by a demon called him a lunatic, and said the disciples could not cure him, in Matthew 17:14-16; but in Mark 9:17 he said his son had a dumb spirit, and in Luke 9:39 'a spirit taketh him.' It was clearly a case of possession: the Lord rebuked the demon, and it departed from him.

In all cases the relief was experienced immediately the demon was expelled; the words used are too explicit to mean aught else than that the persons were possessed, and that the wicked spirits were cast out. The case of Judas Iscariot was somewhat different, inasmuch as it was Satan himself that entered into that wretched man. Luke 22:3 . Here it was more than the mere question of power over man, it was the Adversary standing up against Christ.

Besides the permanent possession of men, there was the unclean spirit of lying prophecy. In the O.T. we have a remarkable instance of a spirit influencing 400 prophets. Ahab was to be enticed to go to war, and a spirit said he would accomplish it. He would go out and be a lying spirit in the mouth of all his prophets. "Now therefore," said Micaiah, "behold, the Lord hath put a lying spirit in the mouth of these thy prophets, and the Lord hath spoken evil against thee." 2 Chronicles 18:20-22 . We do not know the nature of this spirit, nor how he influenced the prophets.

Bibliography Information
Morrish, George. Entry for 'Demoniacs'. Morrish Bible Dictionary. https://www.studylight.org/dictionaries/eng/mbd/d/demoniacs.html. 1897.

Bible Dictionaries Demoniacs

Morrish Bible Dictionary

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Demoniacs