A navel that is neither protruding nor sunken.
A flatmate.
A person with a flat chest, i.e., without breasts.
A flat-bottomed sloop-rigged sharpie.
The operator of a flat joint, or crooked gambling operation.
A flat earther.
A traditional two-dimensional motion picture, as opposed to a deepie.
A flat white (type of coffee).
A flattie spider.
A flat-coated retriever.
A flat store.
A flat marinated cut of meat.
A civil law enforcement officer with a duty to maintain law and order, i.e. bylaw officer, police officer, sheriff, etc.