\Par`al*lel"o*gram\, n. [Gr. ?; ? parallel + ? to
write: cf. F. parall['e]logramme. See {Parallel}, and
{-gram}.] (Geom.)
A right-lined quadrilateral figure, whose opposite sides are
parallel, and consequently equal; -- sometimes restricted in
popular usage to a rectangle, or quadrilateral figure which
is longer than it is broad, and with right angles.
{Parallelogram of velocities}, {forces}, {accelerations},
{momenta}, etc. (Mech.), a parallelogram the diagonal of
   which represents the resultant of two velocities, forces,
   accelerations, momenta, etc., both in quantity and
   direction, when the velocities, forces, accelerations,
   momenta, etc., are represented in quantity and direction
   by the two adjacent sides of the parallelogram.