A simple project I built on the side. There's currently 411k words on the database. Some are fluff—not real words—but removing them would be too time consuming to serve any benefit.
Estimates about the total amount of words in English language vary a lot, because it's hard to define what to include. Do plurals count (flower—flowers)? Words with prefixes (post-this—semi-that)? Alternate forms (to draw—draws—drawing—drawed)? There is an estimated of around 200k words in current use today and Oxford English dictionary has 615k words which includes alternate forms. Highest estimates that include all forms go up to 1 million.
That said, it's periodically checking the internet to see if it can find anything new, so I think it's fair say that unless you're a 16th century apothecary searching for that certain specific potion name, it'll have the words one might be looking for. :-)
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