1, 2. Level, even, flat, smooth suggest a uniform surface without marked unevenness. That which is level is parallel to the horizon: a level surface; A billiard table must be level. Flat is applied to any plane surface free from marked irregularities: a flat roof. With reference to land or country, flat connotes lowness or unattractiveness; level does not suggest anything derogatory. That which is even is free from irregularities, though not necessarily level or plane: an even land surface with no hills. Smooth suggests a high degree of evenness in any surface, especially to the touch and sometimes to the sight: as smooth as silk.

Did you mean angular velocity?