cir·cu·lar / ˈsərkyələr/ (abbr.: cir. or circ.) • adj. 1. having 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.• n. a letter or advertisement that is distributed to a large number of people.DERIVATIVES: cir·cu·lar·i·ty / ˌsərkyəˈlaritē/ n.cir·cu·lar·ly adv.

circular of the form of a circle XV; affecting a ‘circle’ of persons XVII (circular letter); sb. for ‘circular note’ XVIII. — AN. circuler, OF. circulier (mod. -aire), learned alt. of cerclier :- late L. circulāris, f. circulus CIRCLE; further latinized in Eng. (XVI). See -AR.
So circulate †subject to repeated distillation XV; †encircle XVI; move or turn round; pass continuously from place to place XVII. f. pp. stem of L. circulāre, f. circulus; see -ATE 3. circulation XVI. — F. or L.