xiphoid processn. The smallest and lowest of the three divisions of the human sternum, which is cartilaginous in early life but usually ossifies by adulthood. Also called xiphisternum, xiphoid.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.