stag·horn coral (st?g?hôrn?)n. Any of several large reef-building corals having long cylindrical branches that resemble a deer’s antlers, especially Acropora cervicornis of the western Atlantic.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.stag?horn cor?al (?stæg?h?rn) n. any of several stony corals of the genus Acropora, having the skeleton branched like antlers. [1880?85] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.