Gallo-Latin Albiōn (Middle Irish Albbu) is from a Proto-Celtic stem *Alb-i̯en-. Together with other toponyms such as Alpes it may either derive from a Proto-Indo-European root *albh- "white" (also found in Welsh elfydd meaning "world" and in the Germanic Elves), or may be of pre-Indo-European origin.
It is often hypothesised that the Romans took it as connected with albus (white), in reference to the White cliffs of Dover and Alfred Holder's Alt-Keltischer Sprachschatz (1896) unhesitatingly translates it Weissland ("white-land").
The early writer (6th century BC) whose periplus was translated by Avienus at the end of the 4th century AD (see Massaliote Periplus) does not use the name Britannia; he speaks of nesos 'Iernon kai 'Albionon: the islands of the Ierni and the Albiones. Likewise, Pytheas of Massilia (ca. 320 BC) speaks of Albion and Ierne. But Pytheas' grasp of the "Πρεττανικη" (Britanic) archipelago is somewhat blurry, and appears to include anything he considers a western island, including Thule.
By the 1st century AD, the name refers unequivocally to Great Britain. The Pseudo-Aristotelian text De mundo (393b) has:
Ἐν τούτῳ γε μὴν νῆσοι μέγισται τυγχάνουσιν οὖσαι δύο, Βρεττανικαὶ λεγόμεναι, Ἀλβίων καὶ Ἰέρνη
"the largest islands they reached were two, called the Britannic [isles], Albion and Ierne."
Pliny the Elder, in his Natural History (4.16.102) likewise has:
"It was itself named Albion, while all the islands about which we shall soon briefly speak were called the Britanniae."
c900 tr. Bæda's Hist. (1890) I. I. 24 Breoton is garsecges ealond, æt wæs iu geara Albion haten. c1205 Layamon's Brut (1847) 1243 Albion hatte at lond. 1387 TREVISA Higden (Rolls) II. 5 Firste is ilond hite Albion, as it were e white lond. c1399 CHAUCER Purse l. 22 in Wks. (1894) I. 406 O conquerour of Brutes Albioun. a1592 GREENE Fr. Bacon (1594) sig. E2v, As if that Edward gaue me Englands right, And richt me with the Albion diadem. 1593 SHAKES. 2 Hen. VI I. iii. 48 Is this the Gouernment of Britaines Ile? And this the Royaltie of Albions King? 1605 Lear III. ii. 91 Then shal the Realme of Albion, come to great confusion. [1653 J. BOSSUET uvres (1816) XI. 469 L'Angleterre, ah! la perfide Angleterre, que le rempart de ses mers rendoit inaccessible aux Romains.] 1713 POPE Windsor-For. 5 When Albion sends her eager Sons to War. 1757 GRAY Progr. Poesy II. st. iii in Odes 9 When Latium had her lofty spirit lost, They sought, oh Albion! next thy sea-encircled coast. 1841 W. M. THACKERAY in Fraser's Mag. June 711/2 Ferocious yells of hatred against perfidious Albion were uttered by the liberal French press. [1846 R. FORD Gatherings fr. Spain iv. 37 If there be a thing which ‘La perfide Albion’, ‘a nation of shopkeepers’, dislikes,..it is a bankrupt.] 1850 WORDSW. Prel. (1926) x. 239 Since I had seen the surge Beat against Albion's shore. 1903 A. MCNEILL Egregious English 11 The French dislike of perfidious Albion may be reckoned to a great extent an intermittent matter. 1941 H. G. WELLS You can't be too Careful III. viii. 146 There I wasa lovely crossingsaying Adieu to the white cliffs of Albion.