behind someone's back

US /bɪˈhaɪnd ˈsʌm.wʌnz bæk/
UK /bɪˈhaɪnd ˈsʌm.wʌnz bæk/
"behind someone's back" picture
1.

without someone's knowledge or without telling them

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I can't believe she talked about me behind my back.
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They made the decision behind his back.
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be on someone's backbehindstab someone in the backcover someone's backpat someone on the backsomeone's back is turnedget off someone's back