noun
mutual dependence; interdependence
A rare yojijukugo meaning that two parties are so closely connected that they cannot exist without each other, like lips and teeth or the cheek and jawbone. Used in formal or literary contexts.
両国は唇歯輔車の関係にある。
The two countries are in a relationship of mutual dependence.
From classical Chinese, combining the metaphors of lips and teeth (唇歯) and the cheek and jawbone (輔車) to express inseparable mutual dependence.