Etymology of the Word Rhombus

Date: 01/30/2003 at 09:07:39
From: Ms. Judy
Subject: 2D shape

My first grade class would like to know where the word rhombus comes 
from as they find it an unusual word and why the shape is called this.

Date: 01/30/2003 at 09:11:37
From: Doctor Sarah
Subject: Re: 2D shape

Hi Ms. Judy - thanks for writing to Dr. Math.

From Steven Schwartzman's _The Words of Mathematics - An Etymological 
Dictionary of Mathematical Terms Used in English_ (Mathematical 
Association of America):

rhombus (noun), rhombic (adjective):

rhombus is a Latin word borrowed from Greek rhombos. The Indo-European 
root is wer- "to turn, to bend." A native English cognate is wrap. A 
rhombos in Greek was what is known among anthropologists as a bull-
roarer, a small object rapidly swung about on a cord in order to make 
a noise. Such objects were used in religious ceremonies by many 
cultures, not just the ancient Greeks. Apparently the shape of the 
Greek rhombos was akin to what we now call a rhombus: a parallelogram 
with all sides equal.

- Doctor Sarah, The Math Forum
  http://mathforum.org/dr.math/