car·ban·i·on (kär-b?n????n, -???n?)n. An anion in which carbon carries a negative charge and an unshared pair of electrons.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.carbanion (k???bæna??n) n (Chemistry) a negatively charged organic ion in which most of the negative charge is localized on a carbon atom. Compare carbonium ionCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014