Ineffective as a broken comb (9)

I believe the answer is:

toothless

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'ineffective' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

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(Other definitions for toothless that I've seen before include "Lacking power" , "Deprived of power" , "Lacking in force" , "Unable to chew; ineffective (sanction)" .)

I've seen this clue in The Daily Express.

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