The 171,476 figure from OED is used inaccurately in a way that shows a gross misunderstanding of dictionaries and language. The number 171,476 refers to the number of full entries for words in “current use” as defined in the 20-volume Second Edition of the Oxford English Dictionary (OED). It does not represent words. It also does not include all the OED's variant spellings, inflected forms, phrases or run-ons (sub-entries derived from the main entries). Additionally, the OED is by no means a complete inventory of English. In fact, it's probably millions of words short, especially as it has an incredibly slow update cycle. Source: I am a dictionary editor and lexicographer, use OED daily, and know the people who make it.