Noun

Singular rhombus

Plural rhombi or rhombuses

rhombus (plural rhombi or rhombuses)

1. (geometry) A parallelogram having all sides of equal length.

Synonyms

• (in geometry): diamond (not in technical use), lozenge, rhomb

In geometry, a rhombus or rhomb is a quadrilateral whose four sides all have the same length. The rhombus is often called a diamond, after the diamonds suit in playing cards, or a lozenge, though the latter sometimes refers specifically to a rhombus with a 45° angle.

In general, a polygon whose sides have the same length is called equilateral, so a rhombus is an equilateral quadrilateral. Every rhombus is a parallelogram, and a rhombus with right angles is a square. (Euclid's original definition and some English dictionaries' definition of rhombus exclude squares, but modern mathematicians prefer the inclusive definition.)

The English word “rhombus” derives from the Ancient Greek ῥόμβος (rhombos), meaning “spinning top”. The plural of rhombus can be either rhombi or rhombuses.