lan·so·pra·zole (l?n-s??pr?-z?l?)n. A drug of the proton pump inhibitor class, C16H14F3N3O2S, used to treat esophagitis caused by gastroesophageal reflux disease and other disorders associated with increased gastric acid secretion.[lanso-, origin unknown + -prazole, antiulcer drug suff.; see omeprazole.]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.