A list can be found at https://mtg.fandom.com/wiki/Flavor_word, but that's not maintainable. If MTGJSON chooses not to give us a good solution, we can hack it with (^|\n)[a-zA-Z '•]* — , subtract out keywords, chapter abilities, and anchor words by looking for the "choose [a number]" wording vs. "choose [word] or [other word]".