# Dictionary Definition

rhomboid adj : shaped like a rhombus or rhomboid;
"rhomboidal shapes" [syn: rhomboidal]

### Noun

1 a parallelogram with adjacent sides of unequal
lengths; an oblique-angled parallelogram with only the opposite
sides equal

2 any of several muscles of the upper back that
help move the shoulder blade [syn: rhomboid
muscle]

# User Contributed Dictionary

## English

### Noun

### Adjective

rhomboid- resembling, or shaped like a rhombus or rhomboid

#### Derived terms

# Extensive Definition

- This article is about mathematics. For rhomboid muscles in anatomy, see Rhomboid major muscle and Rhomboid minor muscle. For rhomboid in botany see Leaf shape.

In geometry, a rhomboid is a
parallelogram in
which adjacent sides are of unequal lengths and angles are oblique.

A shape like a rhomboid with sides of equal
length (equilateral)
is a rhombus.

A shape like a rhomboid with right angled
corners is a rectangle.

The word Rhomboid which means rhomb-like was
commonly used in the 19th century for a parallelogram which was
neither a rectangle
nor a rhombus. Today it
is more often used for a solid figure with six faces in which each
face is a parallelogram and opposite faces in pairs lie in parallel
planes. Some crystals are formed in 3D rhomboids. It is also
sometimes called a rhombic prism. The term shows up frequently in
science terminology referring to both its two and three dimensional
meaning.

Euclid introduces the term in his Elements in
Book I, Definition 22,

- ''Of quadrilateral figures, a square is that which is both equilateral and right-angled; an oblong that which is right-angled but not equilateral; a rhombus that which is equilateral but not right-angled; and a rhomboid that which has its opposite sides and angles equal to one another but is neither equilateral nor right-angled. And let quadrilaterals other than these be called trapezia.''

- — Translation from the page of D.E.Joyce, Dept. Math. & Comp. Sci., Clark University http://aleph0.clarku.edu/~djoyce/java/elements/elements.html

Euclid never uses the definition of rhomboid
again and introduces the word parallelogram in
Proposition 31 of Book I; "In parallelogrammic areas the opposite
sides and angles are equal to one another, and the diameter bisects
the areas." Heath suggests that rhomboid was an older term already
in use .

## External links

rhomboid in Asturian: Romboide

rhomboid in Catalan: Romboide

rhomboid in Spanish: Romboide

rhomboid in Galician: Romboide

# Synonyms, Antonyms and Related Words

bend,
bias, cube-shaped, cubed, cubic, cubiform, cuboid, diagonal, diced, foursquare, oblique, oblique angle, oblique
figure, oblique line, oblong, orthogonal, quadrangular, quadrate, quadriform, quadrilateral, rectangular, rhombic, scratch comma, separatrix, slant, slash, solidus, square, tetragonal, tetrahedral, transverse, trapezohedral, trapezoid, virgule