vo·mer·o·na·sal organ (v??m?-r?-n??z?l)n. Either of two olfactory sense organs, found near the vomer in certain amphibians, reptiles, and mammals, that detect pheromones and other chemical compounds. In humans, these organs regress during fetal development. Also called Jacobson’s organ.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.