Why is the ninth month called September?
word-forming element meaning "around, all around, on all sides," from Latin circum- a common element in word-formation, from adverb and preposition circum "around, round about," literally "in a circle," probably accusative form of circus "ring" (see circus). In French, the element became circon-; Kitchin points out that con for cum is common even in classical Latin.
Around; about: circumduction.
A prefix meaning "around", as in circumscribe, to draw a figure around another figure.