Uncle is my father's uncle or my mother's uncle: that is to say, if this cousin is born to your father's sister or younger sister, is it called uncle? Uncle? Uncle? If your cousin is from your aunt's house, you should call him uncle. Loose lips. If your cousin's father is your mother's brother, you can call him uncle. If your cousin's mother is your mother's sister, you can call her uncle. If your cousin's mother is your father's sister, you can ask your son-in-law to answer more questions.