Ratu is a title used by Fijians of chiefly rank. An equivalent title, Adi (pronounced [ˈandʒi]), is used by females of chiefly rank. In Malay language, the title Ratu is also the traditional honorific title to refer to the ruler (king or queen) in Javanese culture. Thus in Java, royal palace is called Keraton, constructed from ke- -ancircumfix and Ratu, to describe the residence of Ratu.
Ra is a prefix in many titles (Ramasi, Ramalo, Rasau, Ravunisa, Ratu) and Tu is simply "chief". The formal use of "Ratu" as a title in a name (as in "Sir" in British tradition) was introduced after cession of 1874. Prior to this a Chief would only be known by his birth name and his area specific traditional title.
It all those places it is used as a title preceding the person's name much like "Prince", "Duke", "Earl", "Baron", or "Lord".
The semantics however are a little different in Fijian although the name and title usually reversed, an example:
in English, you would say His Royal Highness (Styling) Prince (address/title) Andrew (name), Duke of York (noble title)
in Fijian, we say, Gone Turgaga Na (Styling) Roko Tui Bau (noble title), Ratu (address/title) Joni Madraiwiwi (name).
The Fijian nobility consists of about seventy chiefs, each of whom descends from a family that has traditionally ruled a certain area. The chiefs are of differing rank, with some chiefs traditionally subordinate to other chiefs. The Tui Kaba clan is regarded as the highest chiefly clan only by people with ties to Bau. They are the heirs of Seru Epenisa Cakobau, the Vunivalu of Bau or Tui Levuka (Paramount Chief of Bau, on the eastern side of Viti Levu, Fiji's most populous island), who was the first chief to unite the entire country under his authority in 1871, when he was proclaimed Tui Viti (King of Fiji). He subsequently ceded the islands to the United Kingdom in 1874. Other prominent chiefly clans include the Vuanirewa (the traditional rulers of the Lau Islands), and the Ai Sokula (the traditional rulers of Vanua Levu).
The Presidency, Vice-Presidency, and fourteen Senate seats are the only constitutional offices whose appointment is controlled by persons of chiefly rank. In a departure from the generally followed British constitutional model (which banned Peers from election to the House of Commons prior to the constitutional reform of 1999), chiefs in post-independence Fiji have always competed for parliamentary seats on an equal footing with commoners. In the years following independence, this favoured the chiefly class, as the common people looked to them as their leaders and generally voted for them. For several elections, many ethnic Fijian members of the House, which is elected by universal suffrage, were of chiefly rank, in recent elections this discrepancy between chiefs and commoners is slowly narrowing, as commoners are becoming better educated and have begun to work their way into the power structure. The chiefs, however, retain enormous respect among the Fijian people. In times of crisis, such as the coups of 1987 and the third coup of 2000, the Great Council of Chiefs has often stepped in to provide leadership when the modern political institutions have broken down. Although the distinction between chiefs and commoners will inevitably continue to lessen, the chiefly institutions are unlikely to disappear any time soon.
Ratu Joni Madraiwiwi; former Vice-President, former High Court Judge and prominent lawyer.
Ratu J.A.R. Dovi; first fully qualified medical doctor.
Lau Islands, Fiji, By Arthur Maurice Hocart, Published 1929, Bernice P. Bishop Museum, Ethnology, 241 pages, Original from the University of Michigan, no.62 1929, Digitized Feb 23, 2007. Page 150 has details on titles like Ratu and Roko and their use