Other forms: loons
A loon is a foolish person, or a diving water bird. A daft loon, loons on the lake, crazy as a loon.
The two senses are unrelated words that collided. The bird is called a diver in Britain and a loon in North America, and its wailing call is the sound of the northern lakes. Crazy as a loon probably comes from that call rather than from the insult.
1nounfoolishA foolish person.
“Some loon was driving the wrong way down the motorway.”
2nounloonA diving water bird.
“The loon dived under the lake and came up again far away.”
loon is a fool, or a bird.
The insult comes from Middle English louen, a rogue. The bird's name is a separate word, probably from an Old Norse word for the diver.
Middle English
louen
English, today
loon
Built from
From Middle English louen, lowen (“rascal; rogue”), probably of Middle Dutch - or Middle Low German - origin. Compare Dutch loen (“simpleton”). Or, related to etymology 2, due to the bird's loud cry. Folk etymology associates it slang-wise with lunatic, though the latter may have influenced it; see loony.
Etymology from Wiktionary, CC BY-SA
Practised in A Song of Ice and Fire