The number of words in the English language is: 1,025,109.8. This is the estimate by the Global Language Monitor on January 1, 2014. The English Language passed the Million Word threshold on June 10, 2009 at 10:22 a.m. (GMT). The Millionth Word was the controversial ‘Web 2.0′.10 Jun 2009
Number of Words in the English Language: 1,025,109.8 …
www.languagemonitor.com/…words/number-of-words-in-the-english-lang…

Merriam Webster
How many words are there in English?
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There is no exact count of the number of words in English, and one reason is certainly because languages are ever expanding; in addition, their boundaries are always flexible. Consider such words as “cannoli” and “teriyaki,” which come from other tongues but are established through use, context, and frequency as English. There are many other thorny considerations that complicate the task of counting individual words and tallying up the language in that way. For example, are all of the inflected forms of a word–for instance, “drive,” “drives,” “drove,” etc.–one word or several separate words?

Similarly, there are twelve different words with the spelling “post” entered in Webster’s Third New International Dictionary, Unabridged; they all have different parts of speech or derivations. Should these twelve be considered one word for the purposes of our reckoning? Some scholars would insist the distinct forms of “post” only be counted once, but others consider each one a separate word that should be counted individually.

Another puzzle: should “port of call,” another Webster’s Third entry, count as a word, even though each of its components is entered separately?

It has been estimated that the vocabulary of English includes roughly 1 million words (although most linguists would take that estimate with a chunk of salt, and some have said they wouldn’t be surprised if it is off the mark by a quarter-million); that tally includes the myriad names of chemicals and other scientific entities. Many of these are so peripheral to common English use that they do not or are not likely to appear even in an unabridged dictionary.

Webster’s Third New International Dictionary, Unabridged, together with its 1993 Addenda Section, includes some 470,000 entries. The Oxford English Dictionary, Second Edition, reports that it includes a similar number.