behind somebody's back

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.See also: back, behind

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 faceSee also: back, behind