水洩不通 [ㄕㄨㄟˇ ㄒㄧㄝˋ ㄅㄨˋ ㄊㄨㄥ; shui3 xie4 bu4 tong1] lit. not one drop can trickle through (idiom); fig. impenetrable (crowd, traffic) ◄ ►