ta·bun (tä?bo?on?) n. A poisonous liquid that is soluble in organic solvents, C5H11N2O2P, used as a nerve agent in chemical warfare. [German, originally a code name.] 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.tabun (t???bu?n) n (Elements & Compounds) an organic compound used in chemical warfare as a lethal nerve gas. Formula: C2H5OP(O)(CN)N(CH3)2[C20: from German, of uncertain origin]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014