stab in the back 1 v. phr. , slang To say or do something unfair that harms (a friend or someone who trusts you). Owen stabbed his friend Max in the back by telling lies about him.
stab in the back 2 n. phr. , slang An act or a lie that hurts a friend or trusting person; a promise not kept, especially to a friend. John stabbed his own friend in the back by stealing from his store. My friend stabbed me in the back by telling the teacher I was playing hooky when I was home sick.