Develop weapon when rights expire (6)

I believe the answer is:

evolve

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'develop' is the definition.
('evolve' can be a synonym of 'develop')

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for evolve that I've seen before include "Unravel" , "Develop by natural selection" , "Gradually acquire new characteristics" , "Develop or change very gradually (6)" , "Reveal a secret" .)

I've seen this clue in The Telegraph.

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