sphinc·ter (sf?ngk?t?r)n. A ringlike muscle that normally maintains constriction of a body passage or orifice and that relaxes as required by normal physiological functioning.[Late Latin sphinct?r, from Greek sphinkt?r, from sphingein, to bind tight.]sphinc?ter·al adj.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.sphincter (?sf??kt?) n (Anatomy) anatomy a ring of muscle surrounding the opening of a hollow organ or body and contracting to close it[C16: from Late Latin, from Greek sphinkter, from sphingein to grip tightly] ?sphincteral adjCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014sphinc?ter (?sf??k t?r) n. a circular band of voluntary or involuntary muscle that encircles and closes an orifice of the body or one of its hollow organs. [1570?80;