Crossword Genius

Worked for nothing when confined (8)

Ross

I believe the answer is:

interned

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'worked' is the definition.
(interning is a kind of working)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for interned that I've seen before include "deprived of freedom" , "With movement restricted" , "Locked up" , "Detained without trial" .)

I've seen this clue in The Irish Times.
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