It's very hard but laundrymaids do it (4)

I believe the answer is:

iron

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

I can't explain the remainder of the clue.

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(Other definitions for iron that I've seen before include "rations in emergency?" , "sort of club" , "Very robust" , "Heavy metallic element" , "Club; element" .)

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

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