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1570s, from Middle French sphincter, from Late Latin sphincter "contractile muscle," from Greek sphinkter "band, anything that binds tight," from sphingein "to squeeze, bind," of unknown origin. First used in anatomical sense by Galen.
sphincter sphinc·ter (sfĭngk'tər)
A ringlike muscle that normally maintains constriction of a body passage or orifice and that relaxes as required by normal physiological functioning. Also called anatomical sphincter.