Crossword Genius

Box without risk (4)

Ross

I believe the answer is:

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'box' is the definition.
(safe is a kind of box)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for safe that I've seen before include "Secure - place in the bank", "Iron box in which to keep money or important papers", "Free from risk", "Secure cupboard", "Strong metal box to store valuables".)