Noun
Alternative form of flatty
(informal) A flat white (type of coffee).
(South Africa) A flat marinated cut of meat.
a chicken flattie
(slang) A flat store.
A flat-bottomed sloop-rigged sharpie.
A flattie spider.
(informal) A traditional two-dimensional motion picture, as opposed to a deepie.
(Internet slang) A flat earther.
(slang) The operator of a flat joint, or crooked gambling operation.
(informal) A flat-coated retriever.
(informal) A person with a flat chest, i.e., without breasts.
(informal) A navel that is neither protruding nor sunken.
(informal) A flatmate.
Source: en.wiktionary.org