Crossword Genius

On a roll, one may have them in hand (4)

Ross

I believe the answer is:

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'hand' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?

I don't understand the rest of the clue.

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(Other definitions for dice that I've seen before include "Random number generators" , "Small cube" , "Cubes used in gambling" , "Take a risk" , "Numbered cube(s)" .)

I've seen this clue in the Evening Standard.
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