亲戚

Erya（尔雅）， the oldest surviving Chinese dictionary or Chinese encyclopedia known dating back to 3rd Century BCE, defined 亲戚 as ““亲指族内，戚言族外” （Qin refers to those in your clan and Qi refers to those outside of your clan). Chinese kinship differentiates paternal and maternal sides. 

To start, you only need to know 5 characters to refer to your parents' siblings: 叔伯姑舅姨。Generally, you don't have to differentiate elder and younger except for your father's brothers. 叔叔 is your father‘s younger brother,  伯伯 is your father's older brother. 姑姑 is  father‘s sister. 舅舅 is your mother's brother and 阿姨 is your mother's sister. Only Children of your father's brothers can have "堂" in front of “哥弟姐妹”， Children from 姑姑， 舅舅 and 阿姨 are have prefix “表”。

The following table are aunts and uncles in Chinese kinship. Spouses are in parenthesis. The children in  green  box use "堂" Ex. 堂弟， 堂妹.  The children (cousins) in orange boxes use "表“ Ex. 表哥， 表姐。