Needed as substitutes? Come off it! (5)

I believe the answer is:

bench

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'it' is the definition.
The definition suggests a singular noun which matches the answer.

I don't understand how the rest of the clue works.

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(Other definitions for bench that I've seen before include "Exhibit at dog show" , "Pew or settle" , "Long seat for judges" , "Plain, stout work-table" , "Magistrates collectively" .)

I've seen this clue in The Guardian.

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