The name Ennis is of Irish origin and is derived from the Gaelic word "innsi," meaning "island" or "river meadow." It is believed to have originated in the medieval period, around the 9th or 10th century AD, when Ireland was divided into various kingdoms and chieftainries.

Ennis was a popular name among the ancient Irish, particularly in the regions of Munster and Connacht. The name was often given to children born near islands or riverside meadows, reflecting the geographical significance of the name's meaning. In Irish mythology, there are references to characters bearing similar names, such as Innis, which further suggests the name's ancient roots.

One of the earliest recorded instances of the name Ennis can be found in the Annals of the Four Masters, a chronicle of medieval Irish history compiled in the 17th century. It mentions an Ennis Ó Conchobhair, who was a prominent figure in the 12th century and a member of the powerful Ó Conchobhair dynasty that ruled Connacht.

Throughout history, several notable individuals have borne the name Ennis. One of the most famous was Ennis Friary, also known as Ennis Abbey, founded in the late 12th century by the O'Brien family in County Clare, Ireland. This Franciscan friary played a significant role in the religious and cultural life of the region for centuries.

Another notable figure was Ennis Tynane (c. 1608-1654), an Irish soldier and captain in the Confederate Catholic forces during the Irish Confederate Wars of the 1640s. He fought against the English Parliamentarian forces and is remembered for his bravery and military prowess.

In the 19th century, Ennis McMillan (1844-1922) was an Irish-American businessman and politician who served as the 22nd Governor of Tennessee from 1899 to 1903. He was influential in promoting economic development and infrastructure projects in the state.

More recently, Ennis Whatley (1924-2005) was an American college basketball coach who led several successful programs, including the University of Alabama and the University of South Alabama. He was inducted into the Alabama Sports Hall of Fame in 1983.

Ennis Esmer (born 1978) is a Canadian actor and writer, best known for his roles in popular television series such as "The Listener," "Blindspot," and "You Me Her." He has received critical acclaim for his performances and has become a recognizable figure in the entertainment industry.