The word Caspian is derived from the name of the Caspi, an ancient people who lived to the southwest of the sea in Transcaucasia. Strabo wrote that "to the country of the Albanians belongs also the territory called Caspiane, which was named after the Caspian tribe, as was also the sea; but the tribe has now disappeared". Moreover, the Caspian Gates, which is the name of a region in Iran's Tehran province, possibly indicates that they migrated to the south of the sea. The Iranian city of Qazvin shares the root of its name with that of the sea. In fact, the traditional Arabic name for the sea itself is Baḥr al-Qazwin (Sea of Qazvin).
In classical antiquity among Greeks and Persians it was called the Hyrcanian Ocean. In Persian middle age, as well as in modern Iran, it is known as درياى خزر, Daryā-e Khazar; it is also sometimes referred to as Mazandaran Sea (Persian: دریای مازندران) in Iran. Ancient Arabic sources refer to it as Baḥr Gīlān (بحر گیلان) meaning "the Gilan Sea".
Some Turkic peoples refer to the lake as Khazar Sea. In Turkmen, the name is Hazar deňizi, in Azeri, it is Xəzər dənizi, and in modern Turkish, it is Hazar denizi. In all these cases, the second word simply means "sea", and the first word refers to the historical Khazars who had a large empire based to the north of the Caspian Sea between the 7th and 10th centuries. Some other Turkic ethnic groups refer to the lake as Caspian Sea. In Kazakh, where it is called Каспий теңізі, Kaspiy teñizi, in Kyrgyz: Каспий деңизи (Kaspiy deñizi), in Uzbek: Kaspiy dengizi.
Renaissance European maps labelled it as Abbacuch Sea (Oronce Fine's 1531 world map), Mar de Bachu (Ortellius' 1570 map), or Mar de Sala (Mercator's 1569 map).
Old Russian sources call it the Khvalyn or Khvalis Sea (Хвалынское море / Хвалисское море) after the name of Khwarezmia. In modern Russian, it is called Каспи́йское мо́ре, Kaspiyskoye more.