(Ger, English) Descendant of Nils, a pet form of Nicholas (people's victory); descendant of Nilles, a pet form of Cornelius (cornel tree); dweller “atten iles," i.e., at the islands.

The surname O’Neil comes from the Irish Gaelic, which is spelt the same. It means ‘son or descendant of Neil (or Neal)’. This first name was originally Nial, and came from the Old Irish ‘niadh’, meaning ‘champion’.

This first name has been popular in Ireland since earliest times. During the Viking invasions its popularity spread throughout the Norse world. In Iceland it became Njal (as seen in The Story of Burnt Njal), and in France it became Nel (or Nele). Here it was later Latinised to Nigellus (meaning ‘black’) which gave over to the variant Nigel.

Various forms of the name appear as a first name in the Domesday Book. Consequently, it soon gave rise to many variant surnames-such as Nelson and Nielson (which developed on its own in Scandinavian from the same first-name source).

The main family clan of the Irish O’Neills are the illustrious O’Neills of Ulster. Here they originated in Tyrone, being descended from the legendary Niall of the Nine Hostages. Other family clans originated further south in Waterford and Carlow— though the name still remains most numerous in the Ulster counties of Tyrone, Antrim and Down. It is Ireland’s tenth most popular name.

Widespread variations on the surname O’Neill range from Neal to Niles, and from Nihill to Nigel. Again, these are largely of Norman origin.

The first mention of any surname related to O’Neill appears in the Domesday Book records for Berkshire in 1086, where one Willelmus filius Nigelli is listed. After this many variations appear in England, but it is unlikely that any of these are of Irish origin until the eighteenth century or even later.

Shane’s Castle, perched on County Antrim’s Lough Neagh, is the ancient stronghold of the O’Neill clan. Thirty feet up the main tower’s south wall there is a sculpture known as the Black Head of the O’Neills. According to ancient legend, the family will come to a tragic end if the head is ever destroyed. The O’Neills also have a banshee in the form of a beautiful young woman who paces back and forth wringing her hands and singing a haunting lament. Her appearance is said to herald the death of any member of the family unlucky enough to hear her wailing.

The internationally known US physicist, Gerard K. O’Neill, has already started work on an idea long popular with science fiction writers, the colonisation of outer space. In 1969 he set out to discredit the possibility in a seminar, discovered it was actually a viable proposition, and convinced NASA, which awarded him a grant in 1975 to pursue the idea.

Hugh O’Neill (c. 1540—1616), the second Earl of Tyrone, was an Irish rebel. Known in his time as ‘The Great Earl’, he led several Roman Catholic uprisings against English rule. Confirmed in his title by James I but under threat of arrest because of a dispute over lands, he fled to Europe in 1607 in an unsuccessful attempt to raise an army. This ‘flight of the earls’, as it is known, marked the end of Gaelic Ulster, which was then anglicised.

The iconoclastic English educator, A.S. Neill (1883—1973), established the experimental boarding school, Summerhill, in the early 1920s. His ideas on liberal education have considerably influenced subsequent development in education at all levels.

Towns and major geographic features which relate to O’Neill are extremely rare. The United States has one-O’Neill, Nebraska.

With about 31,000 namesakes O’Neill is Ireland’s 10th most popular surname. Thus about one out of every 155 residents of Ireland is an O’Neill. (The name is not common enough throughout England, Scotland and Wales to be counted separately.) Around the world O’Neills are most common in Canberra (one in 1,150 families), Sydney (one in 1,575) and Ottawa (one in 1,637). The United States has an estimated total of just over 56,000 O’Neills-making this their 519th most popular surname.