mindmap root((平整)) level applies to a horizontal surface that lies on a line parallel with the horizon: the vast prairies are nearly ~. flat applies to any surface devoid of noticeable curvatures, prominences, or depressions: the work surface must be totally ~. plane applies to any real or imaginary flat surface in which a straight line between any two points on it lies wholly and continuously within that surface: the ~ sides of a crystal. even applies to a surface that is noticeably flat or level or to a line that is observably straight: trim the hedge so that it is ~. smooth applies to a flat or even surface especially free of irregularities: a ~ dance floor. flush applies to a surface or line that forms a continuous surface a line with another surface or line: the river's surface is now ~ with the top of the banks.