at·ro·pine (?t?r?-p?n?, -p?n) also at·ro·pin (-p?n)n. A poisonous, bitter, crystalline alkaloid, C17H23NO3, obtained from belladonna and other related plants. It is used to dilate the pupils of the eyes and as an antispasmodic.[From New Latin Atropa, genus name of belladonna, from Greek Atropos, Atropos; see Atropos.]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.atropine (?ætr??pi?n; -p?n) , atropin or atropian (Pharmacology) a poisonous alkaloid obtained from deadly nightshade, having an inhibitory action on the autonomic nervous system. It is used medicinally in pre-anaesthetic medication, to speed a slow heart rate, and as an emergency first-aid counter to exposure to chemical warfare nerve agents. Formula: C17H23NO3[C19: from New Latin atropa deadly nightshade, from Greek atropos unchangeable, inflexible; see Atropos]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014at?ro?pine (?æ tr??pin, -p?n) n. a poisonous crystalline alkaloid, C17H23NO3, obtained from belladonna or other nightshade plants, used chiefly to relieve spasms or, topically, to dilate the pupil of the eye. [1830?40;