A circle is the round shape formed by all the points equidistant from a center point. This shape can be found everywhere, from the ring on your finger to the performance space in a circus (which sounds suspiciously similar, doesn’t it?).
The Greek word kirkos meant circle, but the word goes back even further to the Proto-Indo-European word kirk, which meant "to bend." The noun refers to that round shape, while the verb form means to move around or surround something. Are you going to knock on the door or just circle around the house all day? If you feel like you haven't been getting anywhere with something, you might say you're "going in circles."