Bread head! (4)

I believe the answer is:

loaf

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But I can't explain it at all! Could you help me understand?

(Other definitions for loaf that I've seen before include "Head (slang) -- be a slacker" , "Bread unit" , "Bread - brain!" , "bloomer, perhaps" , "brains" .)

I've seen this clue in The Times.

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