The name Kaytlin is a modern English variant of the ancient feminine name Caitlin, which has its origins in the Gaelic languages of Ireland and Scotland. The original Gaelic form was Caitlín, derived from the compound words "cait" meaning "pure" and "lín" meaning "young woman" or "little battle."

In its earliest known usage, the name Caitlín appeared in Irish and Scottish records dating back to the Middle Ages. It was particularly popular among families of Celtic descent in regions like Munster, Connacht, and the Scottish Highlands. As the name spread and evolved over centuries, various spellings emerged, including Caitlin, Kaitlyn, and the modern English form, Kaytlin.

While there are no definitive records of the name appearing in ancient texts or religious scriptures, some historians believe it may have been used as a diminutive form of the name Katherine, which has Greek roots and means "pure." However, this connection is speculative, and the name's true origins lie firmly in the Gaelic languages.

One of the earliest recorded individuals with the name Caitlín was an Irish noblewoman from the 12th century, Lady Caitlín Ní Lochlainn, who was a prominent figure in the Uí Lochlainn dynasty of Ulster. Another notable bearer of the name was Caitlín Dubh, a 16th-century Irish chieftain's wife known for her poetry and influence in Gaelic literary circles.

In more recent history, the name gained popularity in the English-speaking world, and several notable figures have borne the various spellings. Caitlin Thomas (1913-1994) was a British author and the wife of the renowned poet Dylan Thomas. Caitlyn Jenner (born 1949) is an American media personality, former Olympic athlete, and transgender rights activist.

Other famous individuals with variations of the name include Kaitlyn Bristowe (born 1985), an American television personality and former contestant on "The Bachelor"; Kaitlin Olson (born 1975), an American actress known for her role in the sitcom "It's Always Sunny in Philadelphia"; and Kaitlyn Dever (born 1996), an American actress who gained recognition for her roles in films like "Booksmart" and "Dopesick."