The 2nd edition of the Oxford Dictionary has 171,476 words in current usage, with 47,156 obsolete words. But this doesn't include suffixes -Oxford estimate there are a quarter of a million distinct English words, excluding inflections, and words from technical and regional vocabulary.
If you want to improve your vocabulary, and personally I find it an addictive game, try the charitable organization
FreeRice. It gives rice to the third world as you play the game plus you learn new words.
AskOxford: How many words are there in the English language?