THESAURUS
sphincter
O, annular muscle, annulus, areola, aureole, chaplet, circle, circuit, circumference, circus, closed circle, corona, coronet, crown, cycle, diadem, discus, disk, eternal return, fairy ring, garland, glory, halo, lasso, logical circle, loop, looplet, magic circle, noose, orbit, radius, ring, rondelle, round, roundel, saucer, vicious circle, wheel, wreath