non·stress test (n?n?str?s?)n. An ultrasound examination of a fetus that measures fetal well-being by correlating fetal movement with changes in fetal heartbeat.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.