Rhomboid in the context of Parallelepiped

The Necker cube is an optical illusion that was first published as a rhomboid in 1832 by Swiss crystallographer Louis Albert Necker. It is a simple wire-frame, two dimensional drawing of a cube with no visual cues as to its orientation, so it can be interpreted to have either the lower-left or the upper-right square as its front side.

In geometry, a parallelepiped is a three-dimensional figure formed by six parallelograms (the term rhomboid is also sometimes used with this meaning). By analogy, it relates to a parallelogram just as a cube relates to a square.

Three equivalent definitions of parallelepiped are

British heavy tanks were a series of related armoured fighting vehicles developed by the UK during the First World War. The Mark I was the world's first tank, a tracked, armed, and armoured vehicle, to enter combat. The name "tank" was initially a code name to maintain secrecy and disguise its true purpose. The tank was developed in 1915 to break the stalemate of trench warfare. It could survive the machine gun and small-arms fire in "no man's land", travel over difficult terrain, crush barbed wire, and cross trenches to assault fortified enemy positions with powerful armament. Tanks also carried supplies and troops.

British heavy tanks are distinguished by a rhomboidal shape with a high climbing face of the track, designed to cross the wide and deep trenches prevalent on the battlefields of the Western Front. Due to the height necessary for this shape, an armed turret would have made the vehicle too tall and unstable. Instead, the main armament was arranged in sponsons at the side of the vehicle. The prototype, named "Mother", mounted a 6-pounder (57 mm) cannon and a Hotchkiss machine gun at each side. Later, subtypes were produced with machine guns only, which were designated "Female", while the original version with the protruding 6-pounder was called "Male".

Spar is an old mining or mineralogy term used to refer to crystals that have readily discernible faces. A spar will easily break or cleave into rhomboidal, cubical, or laminated fragments with smooth shiny surfaces.

The various spar minerals were a historical term among miners and alchemists for any nonmetallic mineral akin to gypsum, known in Old English as spærstān, spear stone, referring to its crystalline projections. Thus, the word spar in mineralogy has the same root as "spear,".