| Sphincter 1. (n.) A muscle which surrounds, and by its contraction tends to close, a natural opening; as, the sphincter of the bladder. 2. (a.) Of, pertaining to, or designating, a sphincter; as, a sphincter muscle. Thesaurus Entries 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 |