His father had threatened disinheritance, but both men had known it was an empty threat.

他父亲威胁要剥夺他的继承权，但是两人都知道这是虚张声势。

《柯林斯英汉双解大词典》

But that may be an empty threat.

但这可能是个空洞的威胁。

youdao

But that may be an empty threat.

但这可能是个空洞的威胁。

youdao