behind (one's) back
In one's absence. The phrase typically suggests wrongdoing or deceit. I can't believe you were gossiping about me behind my back! Tom will be upset that we already made the decision behind his back.
behind someone's back
without someone's knowledge; secret from someone. Please don't talk about me behind my back. She sold the car behind his back, while he was away on vacation.
behind someone's back
Out of one's presence or without someone's knowledge, as in Joan has a nasty way of maligning her friends behind their backs. Sir Thomas Malory used this metaphoric term in Le Morte d'Arthur (c. 1470): "To say of me wrong or shame behind my back." [Early 1300s]
do something behind someone's back
COMMON If someone does something behind your back, they do it secretly, to harm you. It's horrible to have people laughing at you behind your back. He's been arranging all this behind my back.
behind someone's back
without a person's knowledge and in an unfair or dishonourable way.behind somebody’s ˈback
without somebody knowing, especially because they would not like it: I feel guilty about going behind his back and complaining to the boss.People were often very rude about her behind her back. OPPOSITE: to somebody’s face behind (one's) back
In one's absence or without one's knowledge.