Emily Dickinson Lexicon

FLAT, n.

1. A level or extended plain. In America, it is applied particularly to low ground or meadow that is level, but it denotes any land of even surface and of some extent.
2. A level ground lying at a small depth under the surface of water; a shoal; a shallow; a strand; a sand bank under water.
3. The broad side of a blade. Dryden.
4. Depression of thought or language. Dryden.
5. A surface without relief or prominences. Bentley.
6. In music, a mark of depression in sound. A flat denotes a fall or depression of half a tone.
7. A boat, broad and flat-bottomed. A flat-bottomed boat is constructed for conveying passengers or troops, horses, carriages and baggage.