Naib

The word naib (نائب) is an Arabic word meaning someone who is second in command.

It may also mean:

In history
Naib, the name given to the rulers of Massawa, Africa who served the Ottoman Empire from the sixteenth century to the nineteenth century.
Naib, a local leader in Dagestan.

Fiction
Naib, the title given to the leader of Fremen (freemen)  on the planet Arrakis in the science fiction Dune universe written by Frank Herbert. In the story the word "Naib" means servant.