Lunatics. (from the Latin Luna, the moon, because insane persons, especially those who had lucid intervals, were once supposed to be affected by the changes of the moon). This word is used twice, in the New Testament - Matthew 4:24; Matthew 17:15. (Translated epileptic, in the Revised Version).
It is evident that the word itself refers to some disease affecting both the body and the mind, which might or might not be a sign of possession. By the description of Mark 9:17-26, it is concluded that this disease was epilepsy.