## Basic College Mathematics (10th Edition)

Circumference (circum=around): "length $around$ the circle". Diameter (dia=passing through). "distance $passing~through$ the circle". Radius (ray=spoke): "The length of a $spoke$ from the center of a circle to the edge".
We look at the prefixes in each geometry term: Circumference. Prefix: Circum. Meaning: around (e.g. circumvent). Thus circumference means "length $around$ the circle". Diameter. Prefix: Dia. Meaning: passing through (e.g. diagonal). Thus diameter means "distance $passing~through$ the circle". Radius. Prefix: Rad. Meaning: ray or spoke (e.g. radiant). Thus radius means "The length of a $spoke$ from the center of a circle to the edge".