The names Dubrovnik and Ragusa co-existed for several centuries. Ragusa, recorded in various forms since at least the 10th century, remained the official name of the Republic of Ragusa until 1808, and of the city within the Kingdom of Dalmatia until 1918, while Dubrovnik, first recorded in the late 12th century, was in widespread use by the late 16th or early 17th century.
The name Dubrovnik of the Adriatic city is first recorded in the Charter of Ban Kulin (1189). It is mostly explained as dubron, a Celtic name for water (Gaulish dubron, Irish dobar, Welsh dŵr, dwfr, Cornish dofer), akin to the toponyms Douvres, Dover, and Tauber; or originating from a Proto-Slavic word dǫbъ meaning ‘oak’. The term dubrovnik means the ‘oakwood’, as in all other Slavic languages the word dub, dàb, means ‘oak’ and dubrava, dąbrowa means the ‘oakwood’.
The historical name Ragusa is recorded in the Greek form Ῥαούσιν (Rhaousin, Latinized Ragusium) in the 10th century. It was recorded in various forms in the medieval period, Rausia, Lavusa, Labusa, Raugia, Rachusa. Various attempts have been made to etymologize the name. Suggestions include derivation from Greek ῥάξ, ῥαγός “grape”; from Greek ῥώξ, ῥωγός “narrow passage”; Greek ῥωγάς “ragged (of rocks)”, ῥαγή (ῥαγάς) “fissure”; from the name of the Epirote tribe of the Rhogoi, from an unidentified Illyrian substrate. A connection to the name of Sicilian Ragusa has also been proposed. Putanec (1993) gives a review of etymological suggestion, and favours an explanation of the name as pre-Greek (“Pelasgian”), from a root cognate to Greek ῥαγή “fissure”, with a suffix -ussa also found in the Greek name of Brač, Elaphousa.
The classical explanation of the name is due to Constantine VII’s De Administrando Imperio (10th century). According to this account, Ragusa (Ῥαούσιν) is the foundation of the refugees from Epidaurum (Ragusa Vecchia), a Greek city situated some 15 km (9 mi) to the south of Ragusa, when that city was destroyed in the Slavic incursions of the 7th century. The name is explained as a corruption of Lausa, the name of the rocky island on which the city was built (connected by Constantine to Greek λᾶας “rock, stone”).