The term used in the Qur’an for a king is generally malik ملك e.g. whem the Israelites “said to a prophet of theirs, ‘Raise up for us a king'” (Surah ii. 246.)
(1) The word malik is now merely used in Arabia and in Central Asia for a petty chief.
(2) Sultan occurs in the Qur’an for “authority,” or “power,” and not for a king. Surah lxix. 29, “My authority had perished from me.” But it is now the title assumed by the Emperor of Turkey.
(3) Padshah and Shah are Persian words, the ruler of Persia having assumed the title of Shah or King. The word Padshah is derived from pad, “a throne,” and shah, “a lord or possessor,” i.e., “the lord of the throne.” In Hindustani it is Badshah.
(4) Wali, i a title assumed by Muslim rulers, the title being held by the Barakzai rulers of Afghanistan in all legal documents. The word simply means a possessor, or one in authority.
(5) Amir has a similar meaning to Wali, and is a title which is assumed by Muslim rulers, as the Amris of Bukharah and of Kabul. It is derived from ‘amr, “to rule.”
(6) Saiyid, “a lord,” is a title given to the descendants of Muhammad, and is a regal title assumed by the ruler of Zanzibar.
(7) Imam, “a leader,” is the legal title of the head of the Muslims, and it is that given to the successors of Muhammad, who are so called in the Traditions and in Muslim works of law. [IMAM.]
(8) Khalifah, “a vicegerent.” Khalifah, or Caliph, is used for the same regal personage as Imam. [KHALIFAH, RULERS.]
Based on Hughes, Dictionary of Islam