Толковый словарь английского языка Oxford English Reference - parallelogram

n. Geom. a four-sided plane rectilinear figure with opposite sides parallel. Phrases and idioms parallelogram of forces 1 a parallelogram illustrating the theorem that if two forces acting at a point are represented in magnitude and direction by two sides of a parallelogram meeting at that point, their resultant is represented by the diagonal drawn from that point. 2 this theorem. Etymology: F parall{eacute}logramme f. LL parallelogrammum f. Gk parallelogrammon (as PARALLEL, gramme line)