Semidiameter
/ˌsɛmi.daɪˈæmɪ.tər/noun
Half the diameter of a circle or sphere, measured from the center to the edge.
Did you know?It comes from Latin semidiameter, a learned term built from semi- (“half”) + diameter, and the same Greek root behind diameter originally meant a line “measured across” a shape.
Etymological Timeline
Ancient Greek
Greek
diametros
“A line measured across a circle or sphere, from one side to the other.”
Classical Latin
Latin
diametrus
“A diameter, or line passing through the center of a figure.”
Late Latin
Latin
semidiameter
“Half a diameter; the radius of a circle or sphere.”
Middle English
English
semidiameter
“A mathematical term for half the diameter of a circle or sphere.”
Modern English
English
semidiameter
“The distance from the center of a circle or sphere to its boundary.”