Yīn

1. The dark, female, receptive principle that stands in complementary opposition to yáng.

2. Specifically the genitals or anus (the private, concealed parts of the body). For example, (二阴 èr yīn), two yīn, is a collective name for the genitals and anus, (阴头 yīn tóu), and yīn head, denotes the glans penis.