Either way, it's a blunder (4)
I believe the answer is:
boob
I believe this is a double definition.
'either way' is the first definition.
'it's a blunder' is the second definition.
(I've seen this before)
(Other definitions for boob that I've seen before include "Embarrassing mistake" , "Mistake; breast (sl.)" , "Slip" , "Blunder (colloq.)" , "Error" .)