While lunatic is used to designate a crazy or very foolish person, these days we use a much softened sense of this word. “He’s a lunatic” can be said with fondness and admiration; think Bill Murray.
A few centuries back, lunatic and insane were a technical pair. Insanity was a permanent condition, chronic in nature. Lunacy was intermittent; there were periods of lucidity.
But what triggered the bouts of lunacy? The ancient Romans thought they knew: it was the phases of the moon. A waxing moon brought lucidity; a full moon brought out the wolf man in us.
And the Latin word for moon? It was luna, of course.
(substitute @ for AT above)