from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Slang A person regarded as silly or stupid.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Someone who is not very smart or clever.
from the GNU version of the Collaborative International Dictionary of English
- n. a person with confused ideas; incapable of serious thought.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a person with confused ideas; incapable of serious thought
From the compound bird + brain, implying that the brains of birds are small. (Wiktionary)