adjective / adverb / noun
flat
FLAT/flˈæt/
Level across a surface without raised parts.
The tabletop is perfectly flat, with no bumps or ridges.

Etymology
Old Norse flatr already meant flat. Early English uses described something stretched out or lying full-length on the ground, followed by the surface sense of being level, smooth, and without curvature or projection.
In context
Make sure your back is straight and your neck is long. Your feet are flat on the floor.
More examples
- Lay the fabric flat before you cut it.
- Shallow water covers the tidal flats at high tide.
- She wears flats instead of heels for the walk.
Forms
flat · flatter · flattest · flats
flatten verb — To make or become more level.
flatness noun — The quality of having an even surface.