Rhomboid

 ( Types Of Quadrilaterals ) 

Traditionally, in two-dimensional geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are non-right angled.

The terms "rhomboid" and "parallelogram" are often erroneously conflated with each other (i.e, when most people refer to a "parallelogram" they almost always mean a rhomboid, a specific subtype of parallelogram); however, while all rhomboids are parallelograms, not all parallelograms are rhomboids.

A parallelogram with sides of equal length (equilateral) is called a rhombus but not a rhomboid. A parallelogram with corners is a rectangle but not a rhomboid. A parallelogram is a rhomboid if it is neither a rhombus nor a rectangle.

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History Euclid introduced the term in his Elements in Book 1, Definition 22,

Euclid never used the definition of rhomboid again and introduced the word parallelogram in Proposition 34 of Book 1; "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.

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Symmetries The rhomboid has no line of symmetry, but it has rotational symmetry of order 2.

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Occurrence

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In biology In biology, rhomboid may describe a geometric rhomboid (e.g. the rhomboid muscles) or a bilaterally-symmetrical kite-shaped or rhombus outline, as in leaves or .

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In medicine In a type of arthritis called pseudogout, crystals of calcium pyrophosphate dihydrate accumulate in the joint, causing inflammation. Arthrocentesis reveals rhomboid-shaped crystals under a microscope.

In anatomy, rhomboid-shaped muscles include the rhomboid major muscle and the rhomboid minor muscle.

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