noun · the female of an animal, bird, or plant

牝鸡司晨在古代被认为是不祥之兆。

noun · a hole or socket designed to receive a bolt or key; the concave part of a mechanism

这把古锁的牝牡结构依然保存完好。

a deep valley or gorge; often used metaphorically in classical or Taoist texts

谷神不死，是谓玄牝。