It might protect an illegal dealer (5)

I believe the answer is:

fence

I'm a little stuck... Click here to teach me more about this clue!

'dealer' is the definition.
(I know that fence is a type of dealer)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for fence that I've seen before include "Dealer in stolen property" , "[SITTER] on this won't make a decision!" , "Railing" , "use blade" , "Enclosing barrier" .)

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