Radii
/ˈreɪ.di.aɪ/noun
The plural of radius, referring to a straight line from the center to the circumference of a circle.
Did you know?In ancient times, the concept of a radius was not just mathematical; it symbolized the rays of divine illumination radiating from celestial bodies.
Etymological Timeline
Proto-Indo-European
PIE
*reydh-
“to flow, to rise, or to radiate”
Latin
Latin
radius
“a staff, spoke of a wheel, or ray of light”
Medieval Latin
Medieval Latin
radii
“the plural of radius, indicating multiple lines or rays”
16th Century
English
radii
“adopted into English as the plural form of radius in mathematical contexts”