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backstabber - Wiktionary, the free dictionary

From Wiktionary, the free dictionary

From back +‎ stabber.

backstabber (plural backstabbers)

  1. A traitor or hypocrite, such as a co-worker or friend assumed trustworthy but who figuratively attacks when one's back is turned.
    Synonym: snake in the grass
    Antonym: backstabbee
    Hyponym: smiling assassin

a traitor or hypocrite