Either way, it's a careless mistake (4)

I believe the answer is:

boob

I believe this clue is a double definition.

'either way' is the first definition.

'a careless mistake' is the second definition.

'it's' is the link.

(Other definitions for boob that I've seen before include "Embarrassing mistake" , "Mistake; breast (sl.)" , "Error" , "Slip" , "Blunder (colloq.)" .)

I've seen this clue in The Telegraph.

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