[Greek] σεληνιάζομαι (selēniazomai), [Latin] lunaticus: to be “moon struck”, be epileptic; Mt.4:24,Mt.17:15
Background Information:
New Testament: Jesus was proclaiming the gospel of the kingdom and curing every disease and illness among the people. A man brought is epileptic son to Jesus, hoping that Jesus will show pity for him. The man’s son was called a lunatic. Jesus healed his son.
Scripture:
“His fame spread to all of Syria, and they brought to Him all who were sick with various diseases and racked with pain, those who were possessed, lunatics, and paralytics, and He cured them.” Mt.4:24
The writer of this gospel already knew the difference between demonic possession and epilepsy. However, those epileptics were called “lunatics”.
Epilepsy: This medical condition was thought to be caused or influenced by the phases of the moon. The person was thought to be “moon struck.”
Mythology: The Roman moon goddess was Luna. The Greek moon goddess was called Selene. Both Luna and Selene are commonly depicted with a crescent moon.
Conclusion:
Lunatic, lunacy
As crazy at it seems, many thought that epilepsy was caused by the moon. So a lunatic was someone who had epilepsy. Now, the term lunatic has a more negative sense.