SCOWL (Spell Checker Oriented Word Lists) has about 70,000 10-letter words total.  If we limit it to the "large" subset recommended for spellchecking in the U.S., it's about 20,000 10-letter words.  If we then remove proper names, capitalized words, abbreviations, contractions, and possessives, it's about 14,000 words (from "abandoning" to "zygodactyl").\n\nScrabble dictionaries usually have considerably fewer 10-letter words, because they remove words that can't be formed in normal gameplay.  The one I have lists about 50 10-letter words.
How many words with 10 letters are there in the US dictionary?