Old cross hides another one that's worn (6)

I believe the answer is:

oxford

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 oxford that I've seen before include "University city" , "Famous 16" , "City on the Thames" , "Isis their second boat" , "Boat Race's Dark Blues" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.