Definition:Euclid's Definitions - Book I/22 - Quadrilaterals
From ProofWiki
Definition
As Euclid defined it:
- 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 I: Definition $22$)
