Loaf of bread (7)
I believe the answer is:
bloomer
'loaf of bread' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for bloomer that I've seen before include "Loaf of bread" , "Large slip" , "Large loaf; or, a mistake" , "A slangy blunder or flower in blossom" , "rose, say" .)