a·cap·ni·a (?-k?p?n?-?)n. A condition marked by an unusually low concentration of carbon dioxide in the blood and tissues.[New Latin, from Latin acapnus, without smoke (which contains carbon dioxide), from Greek akapnos : a-, not; see a-1 + kapnos, smoke.]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.acapnia (e??kæpn??; ??kæpn??) nthe state of lacking carbon dioxide in the bloodCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014