Wildly or giddily foolish: a lunatic decision. (adjective)
Characterized by lunacy or eccentricity.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "lunatic" in a sentence
"_Another lunatic_, was the thought that flashed through my mind; another lunatic, the slave of a single idea."
"Then there is the reference to the moon the term lunatic derives from luna, the Latin word for moon."
"Vague recollections of Edgar Allan Poe and the works of Charles Reade had surrounded the term lunatic asylum with an atmosphere of feather beds and brutality; the word lunatic conjured up in his mind the idea of a man obviously insane."