A crazy person is an example of a lunatic.
A person who behaves in a really wild and bizarre manner is an example of a lunatic.
Wild and crazy behavior is an example of something that would be described as lunatic behavior.
A lunatic decision.
Origin of lunatic
- Middle English lunatik from Old French lunatique from Latin lūnāticus from lūna moon (from the belief that madness was influenced by the phases of the moon) leuk- in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition