一衣带水
a narrow strip of water
中日两国是～、一苇可航的邻邦。China and Japan are close neighbors facing each other across a narrorw strip of water (or separated only by a strip of water).
一衣带水yī yī dài shuǐ
像一条衣带那样窄的水。形容两地非常近，仅一水之隔。a narrow strip of water, a strip of water