Also defined as
Also known as
Outside the US (one of a few countries that use this definition), this figure is known as a trapezoid.
In order to reduce confusion, when such a quadrilateral is intended, it is probably better to use the term irregular quadrilateral instead.
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 plural of trapezium is trapezia.
The word comes from Latin, in which language it is a neuter noun of the second declension, hence its plural form.