How many words are there in English? A popular method for counting words in a language is to use the total number in a dictionary (or some other corpus). But counting words this way doesn’t tell us anything very interesting about “English”, because not every speaker of English knows every word in the dictionary.
For example, you might know the word beech refers to a tree, but not know how to identify one in the woods. You might know that some governments are jingoistic, but not know which ones or why. Maybe you confuse yams and sweet potatoes all the time.
So does beech count as “part of English” if not every speaker of English knows it, uses it, or understands it? The words you know depend on things like education, job, dialect, how much you read, where you grew up, your hobbies, how much you’ve traveled and so on.