| n. | 1. | (Anat.) A muscle which surrounds, and by its contraction tends to close, a natural opening; |
| a. | 1. | (Anat.) Of, pertaining to, or designating, a sphincter; |
| Noun | 1. | sphincter - a ring of muscle that contracts to close an opening Synonyms: anatomical sphincter, sphincter muscle |
A round muscle that opens and closes to let fluid or other matter pass into or out of an organ. Sphincter muscles keep the bladder closed until it is time to urinate.
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