平面三角形 píngmiànsānjiǎoxíng plane triangle Origin Definitions Defs Strokes Stroke Words Sentences Sents 平面 píngmiàn noun plane (geometry) a flat surface; in mathematics, a surface containing all the straight lines that connect any two points on it三角形 sānjiǎoxíng noun triangle three-sided shape in geometry; also describes things with a similar shape, such as a delta