Solution: Thor's hammer - NYT Crossword

This is an interesting entry; it could be just an academically important reference, an Old Norse term for “lightning,” except that “Thor’s hammer” is a major character in the “Avengers” movies, so there’s now a fleet of people who recognize the reference from popular culture. It’s also an extremely unusual word that looks impossible (for me, at least) to deduce from the crosses — MJOLNIR. Millions of people saw the most recent of these movies and heard the hammer’s name, but I don’t know if its spelling was made evident. (You can see here that some of them were curious enough to go to Google right after that movie came out.)