Diameter
/daɪˈæmɪtər/noun
A straight line passing through the center of a circle or sphere and joining two points on its boundary.
Did you know?Its roots come from Greek *dia-* (“through”) and *metron* (“measure”), so the word originally described the act of measuring right through a shape’s heart.
Etymological Timeline
Ancient Greek
Greek
diametron
“a line measured across a circle or sphere”
Late Latin
Latin
diametrum
“a diameter”
Old French
Old French
diametre
“a diameter”
14th Century
English
diametre
“a straight line through the center of a circle”
Modern English
English
diameter
“a straight line passing through the center of a circle or sphere”