Apparently “passkey” appears in exactly two movie titles (according to IMDB): The Devil’s Passkey (1920) and Passkey to Danger (1946). So it was probably more frequently used in 1934 than now. The poster for the latter implies that a passkey is an enormous six-foot long key. (jk)
Citations are thin, but the original definition (a skeleton key, opens multiple locks) seems at odds with WebAuthn (an individual user’s key for a single website).
Why the heck did “skeleton key” stick around and “passkey” fall into disuse? Sure, it sounds way cooler, but I would assume people who carry skeleton keys would prefer boring, professional terms for things.
It’s good to know you considered it. At the time it didn’t feel fair. But I guess that’s just how it goes with puzzles. There’s not much point to this comment other than maybe it will help someone else avoid the spoilers on the hints page.