Crossword Genius

This, I see, is the deep, dark problem that confronts you (5)

Ross

I believe the answer is:

crypt

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for crypt that I've seen before include "Burial vault" , "Underground room of church" , "Underground church vault" , "Sepulchre" , "Vault beneath a church" .)

Want a hint initially instead of a full solution? Install my app