a·ca·cia (?-k??sh?)n.1. Any of various often spiny trees or shrubs of the genus Acacia in the pea family, having alternate, bipinnately compound leaves or leaves represented by flattened leafstalks and heads or spikes of small flowers.2. Any of several other plants in the pea family, especially of the genus Robinia.3. See gum arabic.[Middle English, from Latin, from Greek akaki?.]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.acacia (??ke???) n1. (Plants) any shrub or tree of the tropical and subtropical leguminous genus Acacia, having compound or reduced leaves and small yellow or white flowers in dense inflorescences. Also called: acacia tree See also wattle142. (Plants) false acacia another name for locust2, locust33. (Plants) gum acacia another name for gum arabic[C16: from Latin, from Greek akakia, perhaps related to ak? point]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014a?ca?cia (??ke? ??) n., pl. -cias. 1. a small tree or shrub of the genus Acacia, of the legume family, having clusters of small yellow flowers. 2. any of several other plants, as the locust tree. 3. gum arabic. [1535?45;