An early use of the word can be found in the Nomina Provinciarum Omnium [Names of All the Provinces] c 312. This is a short list of the names and provinces of the Roman Empire. At the end of this list is a brief list of tribes that were considered to be a growing threat to the empire which included the Scoti - the name for the Irish.  There is also a reference to the word in St Prosper's chronicle of AD 431 where he describes Pope Celestine sending St Palladius to Ireland to preach Ad Scotti in Christum [to the Irish who believed in Christ]. 
Thereafter, periodic raids by Scoti are reported by several later fourth-/early fifth-century Latin writers, namely Pacatus, Ammianus Marcellinus, Claudian and the Chronica Gallica of 452. Two references to Scoti have recently been identified in Greek literature (as Σκόττοι), in the works of Epiphanius, Bishop of Salamis, writing in the 370s. The fragmentary evidence suggests an intensification of Irish raiding from the early 360s, culminating in the so-called "barbarian conspiracy" of 367-8, and continuing up to and beyond the end of Roman rule c.410. The location and frequency of attacks by Scoti remain unclear, as do the origin and identity of the Irish population-groups who participated in these raids. The term Scoti gradually came to embrace all Gaels. In the fifth century, the Gaelic kingdom of Dál Riata emerged on the west coast of Scotland. As this kingdom grew in size and influence, the name was applied to all its subjects – hence the modern terms Scot, Scottish and Scotland.
The etymology of Late Latin Scoti is unclear. It is not a Latin derivation, nor does it correspond to any known Goidelic term the Irish used to name themselves as a whole or a constituent population-group. The implication is that this Late Latin word rendered a Primitive Irish term for a social grouping, occupation or activity, and only later became an ethnonym.
Several derivations have been conjectured but none has gained general acceptance in mainstream scholarship. In the nineteenth century Aonghas MacCoinnich proposed that Scoti came from Gaelic Sgaothaich, meaning "crowd". Charles Oman favoured Gaelic Scuit, with the sense of a "man cut-off" or "broken man", suggesting this was not a general word for Gaels but a band of outcast raiders.
More recently, Philip Freeman has speculated on the likelihood of a group of raiders adopting a name from an Indo-European root, *skot, citing the parallel in Greek skotos (σκότος), meaning "darkness, gloom".
An origin has also been suggested in the English word scot (as in tax), corresponding with an activity involving the old Scandinavian verb sköta used in ceremonies where ownership of land was transferred by placing a parcel of earth in the lap of a new owner, from whence 11th century King Olaf, one of Sweden's first known rulers, may have been known as a scot king.
- Freeman, Philip (2001), Ireland in the Classical World (University of Texas Press: Austin, Texas. ISBN 978-0-292-72518-8
- Rance, Philip (2012), 'Epiphanius of Salamis and the Scotti: new evidence for late Roman-Irish relations', Britannia 43: 227-242
- Philip Freeman Ireland and the Classical World
- Maire and Liam de Paor Early Christian Ireland
- Pacatus, Panegyric 5.1
- Amm. Marc. Res Gestae 20.1.1; 26.4.5; 27.8.5
- Claud. De III cons. Hon. 52-8; De IV cons. Hon. 24-33; De cons. Stil. 2.247-55; Epithal. 88-90; Bell. Goth. 416-18
- Chron. Gall. a. 452, Gratiani iv
- Rance (2012)
- Freeman (2001) 88-106; Rance (2012)
- The Encyclopedia Americana: A Library of Universal Knowledge: Volume 15, (1919) Encyclopedia Americana Corp., University of Wisconsin - Madison
- A. MacCoinnich, Eachdraidh na h-Alba (Glasgow 1867)
- C. Oman, A History of England before the Norman Conquest (London 1910) 157
- Freeman (2001) 93
- Demitz in Throne of a Thousand Years p. 9
- Öknamn och tillnamn på nordiska stormän och kungligheter ISBN 91-87064-21-9 p23 (etymology of epithets of Nordic kings and magnates)