It's not the OED in that the definitions are short, without citation, and without grammatical function or derivation, but it is very fast and has a random function for grazing. Handy for quick lookup and for spelling. Pretty good at figuring out what you intended.
metaglossary.com may take a few seconds longer, but provides excellent information for everyday or formal usage. plus there is that 3d dictionary thats floating around. meh, need more then "fast" to impress me.
