(informal) An insane or very foolish person.

(informal, of a person) Insane. / (informal, of a thing) Very silly, absurd.

(Canada, informal, numismatics) The Canadian dollar coin in common circulation since 1987. / (Canada, informal, by extension) The dollar as the Canadian unit of currency.

plural of loonie / plural of loony

plural of looniness

The state or condition of being loony; craziness, lunacy.

(Britain, Australia, New Zealand, derogatory) Left-wing politicians or activists whose policies or ideas are considered to be ridiculous or too politically correct.

(slang) An ambulance used to take a mental patient away to an institution.

(informal, derogatory) a member of the loony left

(slang) A lunatic asylum.