Editing Angle (section)

==History and etymology==
The word ''angle'' comes from the [[Latin]] word {{Lang|la|angulus}}, meaning "corner". [[Cognate]] words include the [[Greek language|Greek]] {{lang|grc|ἀγκύλος}} ({{Lang|grc-la|ankylοs}}) meaning "crooked, curved" and the [[English language|English]] word "[[ankle]]". Both are connected with the [[Proto-Indo-European language|Proto-Indo-European]] root ''*ank-'', meaning "to bend" or "bow".<ref>{{harvnb|Slocum|2007}}</ref>
<!--Note: ἀγκύλος rather than ἀνκύλος is correct; the γκ is a digraph pronounced [ŋk].-->

[[Euclid]] defines a plane angle as the inclination to each other, in a plane, of two lines that meet each other and do not lie straight with respect to each other. According to the Neoplatonic metaphysician [[Proclus]], an angle must be either a quality, a quantity, or a relationship. The first concept, angle as quality, was used by [[Eudemus of Rhodes]], who regarded an angle as a deviation from a [[straight line]]; the second, angle as quantity, by [[Carpus of Antioch]], who regarded it as the interval or space between the intersecting lines; Euclid adopted the third: angle as a relationship.<ref>{{harvnb|Chisholm|1911}}; {{harvnb|Heiberg|1908|pp=177–178}}</ref><!-- This paragraph is quoted from EB1911, but its source seems to be Heath.-->