There may be a catch in it (4)

I believe the answer is:

trap

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

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for trap that I've seen before include "Control ball" , "Ambush" , "website?" , "Vehicle" , "that may catch a speeding motorist" .)

I've seen this clue in The Globe and Mail and the Evening Standard.

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