Skegoneill Avenue is located in the townland of Skegoneill, from the Ir. Sceitheog an Iarla 'the little thorn-tree of the earl'. According to James O'Laverty, the thorn-tree in question marked the spot where William de Burgo, Earl of Ulster, was assassinated in 1333, but this is uncertain and the connection may be with another earl. The name has been anglicised as if the qualifying element were the surname O'Neill, which is definitely not supported by the historical forms. A similar thing has occurred with Ligoniel, which has no etymological link with the O'Neills.
Skegoneill Avenue is probably not simply named after the townland itself but rather after a house of the same name, marked on the 1st edition of the Ordnance Survey six-inch map (1832-46). It was located close to the modern-day junction of York Road and Skegoneill Avenue.
The street-name is first recorded in the Belfast and province of Ulster directory, 1880. Prior to this, it was part of Buttermilk Loney, a long lane that extended for several miles uphill to Ligoniel. Buttermilk Loney persisted subsequently as an unofficial name for Skegoneill Avenue for many years. The name has recently been given a new lease of life as the name of a short street in Ballysillan corresponding roughly to one of the upper stretches of the historical Buttermilk Loney. Loney is an Ulster Scots word meaning 'lane'.
A related name is Skegoneill Street, which was approved in 1898. This was a short street of terraced houses on the east side of York Road, opposite the end of Skegoneill Avenue. It suffered enormous damage when it was bombed in 1941 during the Belfast Blitz. It was subsequently cleared and the area was used for commercial premises.
Resolved – That the Housing Committee be recommended under the circumstances to approve of the name "Skegoniel Parade" for the street referred to on the Housing Site. (18th November 1924).
"Read letters, dated 24th ult., and 18th inst., from Mr. R. McConnell, 2 Skegoniel Parade, relative to the re-naming of Skegoniel Parade, and the matter was referred to the Surveyor for report". (21st April 1925)