slang To be physically squashed or flattened. I forgot that I had a muffin in my bag, and it's flat as a pancake now.My model of a volcano is as flat as a pancake now that you've sat on it!
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.
Extremely level, especially too much so. For example, There are no hills; this terrain is flat as a pancake. This simile dates from the 1500s and has survived its contemporary, flat as a flounder. It is sometimes used, either disparagingly or ruefully, to describe a small-breasted woman.