Σεληνιάζομαι literally means 'to be moonstruck,' reflecting ancient beliefs that certain ailments (particularly epilepsy) were caused or worsened by the moon's phases. The verb appears in Matthew's Gospel to describe people suffering from severe seizures and convulsions. While the etymology connects the condition to lunar influence (σελήνη = moon), the actual medical condition is epilepsy. Jesus heals a moonstruck boy whose symptoms include falling into fire and water, seizures, and inability to speak—classic epileptic manifestations. The term shows how ancient medical vocabulary often embedded folk explanations of disease.