One "possessed with a devil." In the days of our Lord and his apostles, evil spirits, "daemons," were mysteriously permitted by God to exercise an influence both over the souls and bodies of men, inflicting dumbness (Matthew 9:32), blindness (12:22), epilepsy (Mark 9:17-27), insanity (Matthew 8:28; Mark 5:1-5). Daemoniacs are frequently distinguished from those who are afflicted with ordinary bodily maladies (Mark 1:32; 16:17,18; Luke 6:17,18). The daemons speak in their own persons (Matthew 8:29; Mark 1:23,24; 5:7). This influence is clearly distinguished from the ordinary power of corruption and of temptation over men. In the daemoniac his personality seems to be destroyed, and his actions, words, and even thoughts to be overborne by the evil spirit (Mark, l.c.; Acts 19:15).
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Daemoniac'". "Easton's Bible Dictionary".