: a parallelogram with four equal sides and sometimes one with no right angles
The word "rhombus" comes from Ancient Greek: ῥόμβος, romanized: rhombos, meaning something that spins, which derives from the verb ῥέμβω, romanized: rhémbō, meaning "to turn round and round." The word was used both by Euclid and Archimedes, who used the term "solid rhombus" for a bicone, two right circular cones sharing a common base.
