Radian
/ˈreɪ.di.ən/noun
A unit of angular measure equivalent to the angle subtended at the center of a circle by an arc equal in length to the radius.
Did you know?The term 'Radian' is derived from the Latin word 'radius', meaning 'ray' or 'spoke', linking geometry to light and celestial navigation.
Etymological Timeline
Latin
Latin
radius
“spoke of a wheel or ray of light.”
Early 19th Century
English
radian
“a unit of angular measure based on the radius of a circle.”
Mid 19th Century
English
radian
“formalized definition relating angle to arc length.”
Modern Usage
English
radian
“widely adopted in mathematics and physics for measuring angles.”