third cousin in English dictionary third cousin Meanings and definitions of "third cousin" A person whose closest common ancestor with another person is a great-great-grandparent. noun A person whose closest common ancestor with another person is a great-great-grandparent. third cousin more Grammar and declension of third cousin third cousin ( plural third cousins) third cousin (plural third cousins) more Sample sentences with "third cousin" Declension Stem Match words all exact any Try again Available translations Esperanto French German Italian Kadazan Dusun Lithuanian Norwegian Norwegian Nynorsk Polish Russian Scottish Gaelic Swedish Welsh Authors