The Navajo word naakishchíín (also known by naakishchiin, in some instances) is the word for siblings that are twins.
If you examine the word, you’ll see a number! Specifically naaki- denotes two (of something). The rest of the word, -shchíín, is derived from the same root that forms the verb deeshchííh (“to give birth”).
Twins are prominent figures in Navajo tradition. They are prominent in early creation stories, and also later on in the form of the warrior twins who laid waste to the big monsters.