There was an item a few weeks ago about how many separate words there are in English. David Crystal has various suggestions in his Cambridge encyclopedias - and elsewhere - and you can easily find other figures bandied about by other linguists.
But it's not as easy as it might seem to calculate a precise figure. What do we mean by 'words'? Do we include every morphological variant of a root word, with every possible permutation of affixes? Do we just mean 'headword', as lexicographers term them? Some scientific and other specialist glossaries contain thousands, maybe even millions of entries that never make their way into 'English' dictionaries. So beware of easily swallowing stories like: 'English nears its millionth word'; the picture is more complex and multi-faceted than it appears. Here are two links for more nuanced discussion of this fascinating topic:
Merriam-Webster site on this (a very useful site for exploring in general, btw)