backstabber
SMART Vocabulary: related words and phrases Disloyalty, betrayal & treason
adulterous
backstabber
betrayal
betrayer
break ranksidiom
chicane
deserter
desertion
faithless
faithlessly
faithlessness
false
fifth column
sellout
tergiversation
throw someone to the lionsidiom
throw someone under the busidiom
traitor
treasonable
unfaithfulness
stab someone in the back | American Dictionary
stab someone in the back
idiom
to harm someone who trusts you:
A lot of people in this business think they have to stab each other in the back to succeed.