english
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general::
Phrase(s): *flat as a board [and] *flat as a pancake Cliché very flat. (Also used to describe someone’s chest or abdomen, referring to well-developed abdominal muscles or small or nearly absent breasts or pectoral muscles—in either sex. *Also: as ~.) • Jane was flat as a board until she was sixteen, when she suddenly blossomed. • Lucy can mash an aluminum can flat as a pancake with one blow from her heel.
McGrawhill's American Idioms And Phrasal Verbs