Paganini piece, certainly not sacred! (5)

I believe the answer is:

pagan

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

'sacred' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for pagan that I've seen before include "A heathen, not a Christian" , "One outside the main religions" , "Infidel" , "Non-mainstream religious believer" , "Unbeliever" .)

I've seen this clue in the Evening Standard.

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