John 8:44 Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
The word "demon" isn't used in KJV, but it is in other translations.
When we look at Matthew 7:22 in NLT
On judgment day many will say to me, ‘Lord! Lord! We prophesied in your name and cast out demons in your name and performed many miracles in your name.’
The word "demons" means evil spirits or the messengers and ministers of the devil.
Since the Devil is the father of lies and there is no truth in him, then messengers and ministers of the devil would be messengers of lies.
Therefore, I would conjecture that demon possession means possessing lies in our thoughts.
Proverbs 24:9 The thought of foolishness is sin: and the scorner is an abomination to men.