a leader: one lifted up over others to rule, represent, or speak for them
This is the common biblical word for a recognized leader, built from the verb "to lift up, carry." The picture behind it is of a man raised above the group, either because the people exalt him to that place or because he carries responsibility for them. It is a relational title more than a fixed office: it tells you that this person stands at the head of some body and answers for it, without by itself saying how he got there or how far his power reaches.
Because it is so flexible, the same word covers a tribal chieftain chosen to represent his clan, a foreign king's son, the head of a household, and, in Ezekiel, the coming ruler of the restored nation. The senses below sort these by the kind of body the leader heads and the era that uses the term, but the core is steady throughout: a person set up over a group as its head and spokesman.
The word clusters heavily in two settings. In the wilderness books it names the twelve tribal representatives who act for Israel in the census, the offerings, and the dividing of the land. In Ezekiel it becomes the prophet's preferred title for the ruler of the restored people, deliberately chosen instead of the word for "king."