n. pl. lu·na·cies 1. a. Mental derangement; craziness: "The Indians thought his obsession with giant bones a sign of harmless lunacy" (David Rains Wallace). b. Archaic Intermittent mental derangement attributed to the changing phases of the moon. 2. a. Great or wild foolishness: a policy that proved to be a piece of economic lunacy. b. A wildly foolish or irrational act. [From LUNATIC.] |
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