from The American Heritage® Dictionary of the English Language, 4th Edition
- interj. Used to express disdain for something deemed stupid or obvious, especially a self-evident remark.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- interj. Disdainful indication that something is obvious.
- interj. Indication of perceived stupidity, often used in mockery.
Imitative of an utterance attributed to slow-witted people.(American Heritage® Dictionary of the English Language, Fourth Edition)