Lying or existing in the same plane; coplanar.
From Latin com- (together) plus planar (relating to planes or flat surfaces). This technical term developed in mathematics and geometry, with complanar and coplanar used interchangeably, though coplanar became the standard.
Complanar is basically a synonym nobody uses anymore—it lost the naming war to 'coplanar,' showing how scientific terms standardize and less-common variants fade away even when they're perfectly good words.
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