par·a-hy·drox·y·ben·zo·ic acid (p?r??-h?-dr?k?s?-b?n-z???k)n. An organic acid, C7H6O3, widely used in the preparation of preservatives.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.