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
Farlex Dictionary of Idioms.
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
Collins COBUILD Idioms Dictionary, 3rd ed.
- behind (one's) back
- behind back
- behind somebody's back
- behind someone's back
- go behind (one's) back
- go behind back
- go behind someone's back
- back burner
- backburner
- burner