na-adjective, noun
flat and smooth; smooth; level
Describes a surface that is both flat and smooth, without bumps or roughness. Often used in technical or descriptive contexts.
このテーブルの表面は平滑に仕上げられている。
The surface of this table is finished flat and smooth.
平滑な道を自転車で走るのは気持ちが
It feels good to ride a bicycle on a smooth road.