Caius, Gaius

• Origin: Latin
• Meaning: uncertain
• Gender: Male
• Eng Pron: (KIE-us; GUY-us; KIE)

One of the most common Roman praenomina, the origin of Gaius is uncertain. It has traditionally been connected with the Latin gaudere “to rejoice,” though others have suggested that it may be of unknown Etruscan origin.

Caius is an older spelling of Gaius. In early Latin, the letter C represented both the sounds of C and G, and the traditional abbreviation C. continued to be used for Gaius even after the letter G was introduced into the Roman alphabet.

Gaius was extremely common in Ancient Rome. Its feminine form, Gaia, was likewise well established and the two names became part of a traditional Roman marriage formula. According to the ancient writer Plutarch, a bride upon entering her husband’s home would say, Ubi tu Gaius, ego Gaia — “Where you are Gaius, I am Gaia.”

Gaius was the praenomen of Gaius Julius Caesar, as well as his adopted son Gaius Octavius, better known as Augustus. Other notable ancient bearers include the historian Gaius Cornelius Tacitus and the naturalist Gaius Plinius Secundus, better known as Pliny the Elder.

The name also appears several times in the New Testament, including a Gaius who was a companion of Saint Paul. It was later borne by several early Christian saints and Pope Caius, who served as Bishop of Rome in the 3rd century.

Caius survived as a given-name in Britain and elsewhere in Europe, though it was never particularly common. The Welsh Kay has sometimes been linked with Gaius. The name has a long-standing association with England through Gonville and Caius College, Cambridge, which was refounded in the 16th century by the English physician John Caius. Caius can also be found as a given-name in 19th-century British and North American records.

The European name Kai is sometimes considered a later variation or short form of Caius/Gaius, though Kai has several other possible and unrelated origins.

Caius has experienced something of a revival in recent years. Its increased use in both the United States and England may have been helped by the Twilight series, which features Caius as one of the leaders of the Volturi, while its resemblance to the extremely popular Kai likely contributed to its continued rise. The name also fits with the recent fashion for ancient Roman names such as Atticus, Cassius and Augustus.

Caius recently appeared in the U.S. Top 1000, coming in at #927, while in England & Wales it currently ranks at #976 (2025).

Its Lithuanian form of Kajus currently ranks as the 14th most popular male name in Lithuania (2025).

Others forms and usages

• Ghayus غايوس (Arabic)
• Gayos Գայոս, ܓܐܝܘܣ (Armenian, Assyrian)
• Kaio (Basque)
• Kae (Breton)
• Gaij Гаий (Bulgarian, Russian)
• Gai (Catalan, Occitanian)
• Gaios Ⲅⲁⲓⲟⲥ, Γάϊος (Coptic, Greek)
• Kajo (Croatian)
• Kajus (Dutch, Finnish, German, Lithuanian, Polish)
• Kay (Dutch, Swedish, Welsh)
• Caius (English, Latin)
• Kaius (Finnish, German)
• Caïe, Caïus (French)
• Gaio (Galician, Italian, Portuguese)
• Gaioz გაიოზ (Georgian)
• Cajus (German)
• Gajus (German, Polish)
• Kájusz (Hungarian)
• Caio (Italian, Portuguese)
• Kajs (Latvian)
• Gaju (Maltese)
• Gajusz (Polish)
• Kaio (Portuguese – Brazilian)
• Gaiu (Romanian)
• Caiu (Sicilian)
• Gaj (Slovene)
• Cayo (Spanish)
• Hai Гай (Ukrainian)

Medieval Polish diminutive forms include Gasz, Gaszek, Gaszko.

Sources

• https://www.behindthename.com/name/caius
• https://pl.wikipedia.org/wiki/Gajusz_(imi%C4%99)
• https://fr.wikipedia.org/wiki/Ca%C3%AFus_(pape)#cite_note-1