The baby name Caius blends two stylish sounds and a joyful, exuberant meaning.
Thanks to Shannon for suggesting Caius as our Baby Name of the Day.
WHAT DOES THE NAME CAIUS MEAN?
The exact origins of the baby name Caius are open to debate.
Chances are it has Etruscan roots – that’s the even older civilization that predates Ancient Rome. Words from fascinate to mundane have Etruscan roots.
Romans preferred Gaius, but it’s the same name. Or not. Both Cae and Cai appear to have been given names, or at least name elements, used in their language.
So what does it mean?
- The Latin word caesius referred to a light blue color, usually someone’s eye.
- Caelum means sky or heaven, and Caelus was a Roman god of the sky. And, of course, suggests the color blue, too.
Instead, for centuries, we’ve linked Gaius with the Latin gaudere, to rejoice. The baby name Caius is almost always said to mean “happy.”
Whether that’s the name’s actual root, or a folk etymology that developed later is impossible to say.
Also worth noting: Cai occurs in plenty of languages, including Welsh. Sir Kay in the stories of King Arthur and Camelot, takes his name from the Welsh Cai.
Kay and Cai, in turn, likely came from Gaius.
CAIUS THROUGH THE AGES
Gaius and Caius appear steadily in the historical record.
- The first Roman emperor was born Gaius Octavius – but he reigned as Julius Caesar.
- During the 3rd century, a Bishop of Milan answered to Caio, and a different man became Pope Caius in the year 283.
Shakespeare wrote Coriolanus about the historical figure Caius Martius. He also used Caius as a character name in The Merry Wives of Windsor.
Then there’s Dr. John Caius, immortalized in the name of a residential college at Cambridge University. Back in 1348, Gonville Hall was founded at Cambridge. It was struggling when Dr. Caius came along in 1559. He served as master of the college, and left it much expanded, with quite a bit of cash. It’s now known as Gonville & Caius College, typically abbreviated to just Caius, pronounced like Keys.
All of this makes the baby name Caius feel storied and smart.
THE RISE OF KAI
And then there’s that Kai sound.
A Top 100 staple, Kai been steadily rising since the 1980s. While plenty of origins and possible, the Hawaiian word for ocean is the most obvious source.
Along the way, names like Malakai, Cairo, Kaizen, and Zakai have entered the US Top 1000, too.
ANCIENT NAMES
We also love names ending with S. Some, like Atticus, combine ancient sound with 20th century pop culture. Others feel new and freshly discovered for parents now.
Caius is a little of both.
HOW POPULAR IS THE NAME CAIUS?
In the year 2025, the baby name Caius debuted in the US Top 1000 at #927. That works out to 254 births.
Other similar names weren’t quite as common:
- 216 boys were named Kaius. Celebrity stylish Rachel Zoe named her son Kaius-with-a-K in 2014.
- Another 31 were called Gaius.
Caius is occasionally heard in England, but it’s quite rare in much of the world.
ANCIENT UP-AND-COMER
The baby name Caius fits wtih so many trends, but it’s not trendy. How could it be, when the name dates back to Julius Caesar?
It’s an obvious formal name for Cai and Kai, an alternative to other s-enders like Marcus or Cassius.
If you’re looking for something familiar, but seldom heard, the Caius might be the perfect name for your family.
What do you think of the baby name Caius?
First published on February 13, 2014, this post was revised and updated on May 20, 2026.
We picked this name but spell it Kaias as a reference to our family connection to Hawaii. Our son is 8 and some people love it and others warm to it later on. It’s been tricky to deal with the spelling at times but when we explain the meaning of happiness and the Hawaiian homage people seem to like it. Plus the fact that it is a modern play on a name with old origins intrigues others. I love his name. It’s strong, unique and suits him! He is Kaias.
I only like the K spelling, Kaius.
I think this is so handsome, and with the nn Cai especially, extremely usable.
Thanks for covering this name from my boyfriend’s shortlist! I’ll admit that I’m ambivalent about this one, but the storied origins are pretty convincing. I like the idea of “Cai” as a nickname. Definite preference for the C spelling–K seems unnecessarily variant–and I have to admit I’m getting excited about the possibility of Caia for a girl.
Generally, I love the strength and intensity of Latin-derived names with the “us” ending. Caius is one that seems especially wearable (compared with, for instance, Amadeus or Aurelius).
Having a hard time understanding how the “keys” pronunciation can come from the given spelling, I will say.
What about the band Kyuss? That’s what I instantly thought of.
Love Caius and Gaius! The only problems I see are the pronunciation issues with Brits more likely to say “keys” for Caius college. While I don’t love Kaius, it helps clear up the pronunciation a bit. Gaius, though, is by far my fave. I’ve seen people on other sites comment that it sounds too much like gay-ass (oh, the teasing potential), but I only know the guy-us pronunciation (mostly from Battlestar Galactica). I’d love to see Gaius or Caius on a baby. Unfortunately they’re not my husband’s style, so they’re out for me, but I can still push for others to use them 🙂