sphincter

noun

Etymology: Etymology tree Late Latin sphinctērlbor. English sphincter Learned borrowing from Late Latin sphinctēr (“the muscle of the anus”), from Ancient Greek σφῐγκτήρ (sphĭnktḗr, “lace, band; contractile muscle”), ultimately of Pre-Greek origin. Possibly related to sphinx (“the strangler”).

1. A ringlike band of muscle that surrounds a bodily opening (such as the anus or the openings of the stomach), constricting and relaxing as required for normal physiological functioning.

   “the sphincter of the bladder”

   “the iris sphincter in the eye”