撑腰 (chēngyāo): to back someone up

Meanings

Yǒu nǐ gěi wǒ chēngyāo, wǒ shénme dōu bù pà.

With you backing me up, I fear nothing.

Tā zhàng zhe yǒu shàngjí gěi tā chēngyāo, xíngshì yuèlái yuè xiāozhāng.

Relying on his superiors to back him up, he became increasingly arrogant.

Méiyǒu rén gěi nǐ chēngyāo, nǐ gǎn zhème zuò ma?

Without anyone backing you up, would you dare to do this?

memory

撑 means to prop up or support; 腰 is the waist/lower back — to prop up someone's back is to give them the support they need to stand firm.

撑 chēng

腰 yāo