do something behind someone'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

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.
See also: back, behind, something
Full browser ?