Trader, righteous liberal (7)

I believe the answer is:

copious

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'liberal' is the definition.
(both can mean ample or generous)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for copious that I've seen before include "Large in number or quantity" , "Redundant" , "Ample" , "abundance" , "Providing loads of" .)

I've seen this clue in The Guardian.

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