Entry 3 senses · 2 variants Webster, 1913

loony

/(lo͞on"y̆)/ · loon·y · IPA /ˈluːni/

01 a. Crazy; insane; lunatic; mentally unsound.

1.
Crazy; insane; lunatic; mentally unsound.[Low, U.S.]
2.
Very foolish; very impractical; as, loony ideas.

02 n. someone mentally deranged and possibly dangerous.

1.
someone mentally deranged and possibly dangerous.

Syn. crazy, looney, weirdo, psycho.