lunacy

/ˈlunəsi/

Other forms: lunacies

Lunacy is acting silly or stupid. Your mom might yell, "It's lunacy to go out in the snow wearing those flip flops!"

Some people use the noun lunacy when they talk about actual mental instability, although this is considered old fashioned and outdated. It's much more common to describe the lunacy of someone who does something ridiculous or foolish. While adopting a cat from the animal shelter might be a great idea, adopting all thirty cats from the shelter would be lunacy. Lunacy comes from lunatic, originally "affected with periodic insanity, dependent on phases of the moon."

Definitions of lunacy

1. noun

   foolish or senseless behavior
   synonyms: craziness, folly, foolery, indulgence, tomfoolery

   types:

   meshugaas, mishegaas, mishegoss

   (Yiddish) craziness; senseless behavior or activity

   buffoonery, clowning, frivolity, harlequinade, japery, prank

   acting like a clown or buffoon

   schtick, schtik, shtick, shtik

   (Yiddish) a prank or piece of clowning

   type of:

   caper, frolic, gambol, play, romp

   light-hearted recreational activity for diversion or amusement
2. noun

   obsolete terms for legal insanity
   synonyms: insaneness, madness

   type of:

   insanity

   relatively permanent disorder of the mind