Royal and noble ranks
Traditional rank amongst European royalty, peers, and nobility is rooted in Late Antiquity and the Middle Ages. Although they vary over time and between geographic regions (for example, one region's prince might be equal to another's grand duke), the following is a reasonably comprehensive list that provides information on both general ranks and specific differences.
Ranks and titles
Sovereign
The word monarch is derived from the Greek μονάρχης, monárkhēs, "sole ruler" (from μόνος, mónos, "single" or "sole", and ἄρχων, árkhōn, archon, "leader", "ruler", "chief", the word being the present participle of the verb ἄρχειν, árkhein, "to rule", "to lead", this from the noun ὰρχή, arkhē, "beginning", "authority", "principle") through the Latinized form monarcha.
The word sovereign is derived from the Latin above.
Autocrat is derived from the Greek αὐτοκράτωρ: αὐτός ("self") and κρατείν ("to hold power"), and may be translated as "one who rules by himself".
Note that many titles listed may also be used by lesser nobles – non-sovereigns – depending on the historical period and state. The sovereign titles listed below are grouped together into categories roughly according to their degree of dignity; these being: imperial (Emperor, Empress, etc), high royal (King of Kings etc), royal (King/Queen, sovereign Grand Duke or Grand Prince, etc), others (sovereign Prince, sovereign Duke, etc), and religious.