n. In Roman antiquity, a large, oblong, roofless inclosure, used especially for horse- and chariot-races.n. In modern times, a place of amusement where feats of horsemanship and acrobatic displays form the principal entertainment; the company of performers in such a place, with their equipage; the entertainment given.n. In England, the space formed at the intersection of two streets by making the buildings at the angles concave, so as to give the intervening space the form of a circle: as, Oxford Circus, Regent Circus, in London.n. An inclosed space of any kind; a circuit.n. [capitalized] In ornithology, a genus of diurnal birds of prey, the harriers, typical of the subfamily Circinæ (which see)