When is a word a word? According to most dictionaries, there are about 600,000 words in English, but the Global Language Monitor reports that it has so far tracked about 900,000, and that a new word is added to the English language every 98 minutes.
Paul JJ Payack, president and chief word analyst at the Monitor, quotes the Middle English definition of a word as 'a thought spoken'..."which means if I say a word, and you understand me, it's a real word."
I read about this on Boing Boing. The original article at Smithsonian.com explains the difference between the methods used by traditional dictionaries and the algorithm used by Global Language Monitor, who expect the millionth English word to be coined around April 2009.