How many sides does a rhombus have?

In Euclidean geometry, a rhombus (plural rhombi or rhombuses) is a simple (non-self-intersecting) quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length. The rhombus is often called a diamond, after the diamonds suit in playing cards which resembles the projection of an octahedral diamond, or a lozenge.

The word "rhombus" comes from Greek (rhombos), meaning something that spins, which derives from the verb ῥέμβω (rhembō), meaning "to turn round and round." The word was used both by Euclid and Archimedes, who used the term "solid rhombus" for two right circular cones sharing a common base.