姑 refers specifically to the father's sister (paternal aunt), not the mother's sister (which is 姨). It can also mean the husband's sister (sister-in-law, often in compounds like 小姑) and, in a religious context, a Buddhist nun (尼姑). In modern Chinese, 姑 is frequently used in kinship compounds such as 姑姑, 姑妈, and 姑子.