# Definition:Quadrilateral/Oblong

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## Definition

An **oblong** is a quadrilateral whose angles are all right angles, but whose sides are *not* all the same length:

## Also known as

The word **oblong** is rarely seen nowadays.

**Rectangle** is the term usually used instead, unless it is essential to emphasise that such a quadrilateral is *not* a square.

## Euclid's Definitions

In the words of Euclid:

*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 equal to one another but is neither equilateral nor right-angled. And let quadrilaterals other than these be called**trapezia**.

(*The Elements*: Book $\text{I}$: Definition $22$)

## Sources

- 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next):**oblong** - 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next):**oblong**