Close cousin

If two things are related to another by similar natures or origins, they can be called “close cousins.” This term comes from the relationship between two people in the same extended family. A child of your uncle or aunt is your cousin. For a time, researchers had suspected there was water on the Moon, but they were not able to tell whether what they were seeing was water or water’s “close chemical cousin,” hydroxy. Water and hydroxy have similar natures, so they can be called “close cousins.” Plantains are a “close cousin” of bananas.