Of or relating to a circle. Shaped like or nearly like a circle; round. Moving in or forming a circle. Circuitous; roundabout: took a circular route to the office. Using a premise to prove a conclusion that in turn is used to prove the premise: a circular argument. Defining one word in terms of another that is itself defined in terms of the first word. Addressed or distributed to a large number of persons. A printed advertisement, directive, or notice intended for mass distribution.