use your head phrase
to think carefully in order to understand something or to avoid making a mistake
Use your head: why would he say something like that if he was guilty?
Thesaurus: to think carefully or a lot about thingssynonym
Main entry: use
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use your ˈhead idiom
(BrE also use your ˈloaf) (informal) used to tell sb to think about sth, especially when they have asked for your opinion or said sth stupid
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‘Why don't you want to see him again?’ ‘Oh, use your head!’
From rhyming slang, in which loaf of bread stands for ‘head’.Useful english dictionary. 2012.