pace·mak·er (p?s?m??k?r)n.1. Sports One who sets the pace in a race. Also called pacer, pacesetter.2. A leader in a field: the fashion house that is the pacemaker. Also called pacesetter.3. a. A part of the body, such as the mass of muscle fibers of the sinoatrial node, that sets the pace or rhythm of physiological activity.b. Any of several usually miniaturized and surgically implanted electronic devices used to stimulate or regulate contractions of the heart muscle.pace?mak?ing adj. & n.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.pacemaker (?pe?s?me?k?) n1. (General Sporting Terms) a person, horse, vehicle, etc, used in a race or speed trial to set the pace2. a person, an organization, etc, regarded as being the leader in a particular field of activity3. (Anatomy) Also called: cardiac pacemaker a small area of specialized tissue within the wall of the right atrium of the heart whose spontaneous electrical activity initiates and controls the beat of the heart4. (Medicine) Also called: artificial pacemaker an electronic device for use in certain cases of heart disease to assume the functions of the natural cardiac pacemakerCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014pace?mak?er (?pe?s?me? k?r) n. 1. pacesetter. 2. an electronic device surgically implanted beneath the skin to provide a normal heartbeat by electrical stimulation of the heart muscle. 3. any specialized body tissue governing a rhythmic physiological activity, esp. the sinoatrial node that regulates heartbeat. [1880?85] pace?mak`ing, n. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.pace·mak·er (p?s?m??k?r) An electronic device that is surgically implanted to regulate the heartbeat.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.