In the late 1990s, a friend told me she had used the word “exponentially” in a debate with her brother-in-law. “That’s not a word!” her brother-in-law insisted. “Of course it is,” my friend replied.

The dictionary isn’t forever. Here’s the lowdown on why certain words are not in the dictionary and how they got removed. If you, too, have been left puzzled by words not in the dictionary—even ones ...

How many words are there in the English language? Trying to answer this question may take longer than actually getting a dictionary and counting them one by one. It depends on how you define “words” ...