The words Dune borrowed

Mahdi

“The guided one.” In Islam, a figure many Muslims expect near the end of time, who will bring justice. In Dune, Paul is a manufactured messiah built from propaganda: not the Mahdi of Islam. Hebrew has its own word for the hoped-for king, Mashiach, “anointed one”, from which English gets “Messiah”.

Lisān al-Ghayb

“The tongue of the Unseen.” Al-ghayb is what only God knows; the Qur'an says “with Him are the keys of the unseen” (6:59). The New Testament speaks of the unseen too: “Now faith is assurance of things hoped for, proof of things not seen” (Hebrews 11:1, WEB).

Muad'Dib

From muʾaddib, “one who teaches”, “one who trains in good manners”. Adab means courtesy and culture: the teacher shapes character, not just knowledge.

Usul

“Principles, foundations”, as in uṣūl al-fiqh, the principles of Islamic law. In Dune it is Paul’s private name among the Fremen, “the base of the pillar”.

Jihad

In Dune, a galaxy-wide holy war. In Arabic, jihād means striving: ethical effort, and in some cases legitimate defence. Sufi teachers speak of the greatest jihad as the struggle with one's own self, jihād al-nafs. The Hebrew Bible praises the same victory: “He that is slow to anger is better than the mighty; And he that ruleth his spirit than he that taketh a city” (Proverbs 16:32, JPS 1917).

Shai-Hulud

Often explained as Arabic shayʾ khulūd, “thing of eternity”. Lovely, but not confirmed. We say so.