backstabbing
back·stab
(băk′stăb′)tr.v. back·stabbed, back·stab·bing, back·stabs
To disparage or criticize (someone), usually when that person is absent.
back′stab′ber n.
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.
backstab
(ˈbækˌstæb)vb (tr)
to attack in a deceitful manner
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014