rhombus

Etymology

Learned borrowing from Latin rhombus, from Ancient Greek ῥόμβος (rhómbos, “rhombus, spinning top”). Doublet of rhomb and rhumb.

noun

1. (geometry) A parallelogram having all sides of equal length.
   1. The rhombus diamond, as one of the suits seen in a deck of playing cards ( or ).
2. In early Greek religion, an instrument whirled on the end of a string similar to a bullroarer.
   The Greeks also used an instrument called a rhombus, or witches' wheel. As the wheel spun round, it was thought that influence was gained over certain people or circumstances. 1936, Rollo Ahmed, The Black Art, London: Long, page 58
3. (zoology, now rare) Any of several flatfishes, including the brill and turbot, once considered part of the genus Rhombus, now in Scophthalmus.
   the greedy Tuberon or Shark arm'd with a double row of venemous teeth pursues them, directed by a little Rhombus, Musculus or pilot-fish that scuds to and fro to bring intelligence …. 1638, Thomas Herbert, Some Yeares Travels, section I
4. (zoology, archaic) Snails, now in genus Conus or family Conidae.