Philosopher said 'Shut up!' (4)

I believe the answer is:

lock

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'shut up' is the definition.
(I know that shut up can be written as lock)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for lock that I've seen before include "element in pack" , "section of canal" , "Strand of hair" , "Security device - bit of hair" , "part of 10 [CANAL]" .)

I've seen this clue in The Telegraph.

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