Ghent University in Belgium has created an online, almost arcade-game-like test of word knowledge.
How many English words do you know? With this test you get a valid estimate of your English vocabulary size within 4 minutes and you help scientific research.
In this test you get 100 letter sequences, some of which are existing English words (American spelling) and some of which are made-up nonwords. Indicate for each letter sequence whether it is a word you know or not by pressing the F or J key.