ho·mat·ro·pine (h?-m?t?r?-p?n?)n. An anticholinergic drug derived from tropine, C16H21NO3, used in its bromide form to dilate the pupil of the eye and in combination with hydrocodone to prevent overdosage of that drug.[hom(o)- + atropine.]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.