loony

UK: /ˈluːni/ US: /ˈluni/ ,(lo̅o̅′nē)

Inflections of 'loony' (adj):

loonier

adj comparative

looniest

adj superlative

Inflections of 'loony' (n): npl: loonies

WordReference Random House Learner's Dictionary of American English © 2025

loon•y or loon•ey /ˈluni/   adj., -i•er, -i•est, n., pl. -ies or -eys. [Informal.]
adj. 

1. lunatic;
   insane.
2. extremely foolish.

n. [countable]

3. a lunatic.

WordReference Random House Unabridged Dictionary of American English © 2025

loon•y  (lo̅o̅′nē), adj., loon•i•er, loon•i•est, n., pl. loon•ies. [Informal.]
adj. 

1. lunatic;
   insane.
2. extremely or senselessly foolish.

n. 

3. a lunatic.

Also, looney, luny. 

• lun(atic) + -y² 1860–65

loon′i•ness, n. 

loon•y  (lo̅o̅′nē), n., pl. loon•ies. 

1. loonie.

Collins Concise English Dictionary © HarperCollins Publishers::

loony, looney, luny / ˈluːnɪ/ adjective (loonier, looniest, lunier, luniest)

1. mentally disordered
2. foolish or ridiculous

noun (loonies, looneys, lunies)

1. a foolish person
2. a mentally disordered person

ˈlooniness, ˈluniness noun