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DictionaryloonFoolish or eccentric person
noun

loon

An insulting term for someone considered foolish or eccentric.

She calls me a loon for swimming in the lake in January.

Etymology
loonEnglisha foolish or worthless person

The insult has an older personal meaning. Later association with loony reinforced it; the waterbird-name is separate.

More examples

  • Only a loon would try to fix a toaster with a fork.
  • They dismiss him as a loon because of his strange inventions.
  • The neighbors call us loons for hanging Christmas lights in July.

Forms

loon · loons

Similar words

fool
Emphasizes poor judgment rather than odd or eccentric behavior.
eccentric
Describes an unusual person without necessarily expressing insult or contempt.
nut
A similarly informal insult suggesting irrational or eccentric behavior.