Around or about.
[Latin circum, around.]
Many words in this form have been adopted, usually in a figurative sense, from Latin words already containing it: to circumvent (Latin venire, to come) is to avoid or find a way around some obstacle; to be circumspect (Latin specere, to look) is to be wary or careful; circumscribe (Latin scribere, write) can still literally mean to draw a line round something, but usually means to restrict within limits.
To circumnavigate the world is to travel all the way round it; a circumcircle is a circle that touches all the vertices of a geometrical figure. Several adjectives denote moving around a celestial body, such as circumsolar (the Sun) and circumlunar (the Moon); circumpolar refers to moving around the pole, especially a circumpolar star, one that never sets.