circular

adjective

• 1having the form of a circle:the building features a circular atrium
• (of a movement or journey) starting and finishing at the same place and often following roughly the circumference of an imaginary circle:a circular walk

• 2 Logic (of an argument) already containing an assumption of what is to be proved, and therefore fallacious.

• 3 [attributive] (of a letter or advertisement) for distribution to a large number of people.

noun

• a letter or advertisement that is distributed to a large number of people.