How Well Do You Know English Slang?
c.1200, from Late Latin Saxonem (nominative Saxo; also source of French Saxon, Spanish Sajon, Italian Sassone), usually found in plural Saxones, from a Germanic source (cf. Old English Seaxe, Old High German Sahsun, German Sachse "Saxon"), with a possible literal sense of "swordsmen" (cf. Old English seax, Old Frisian, Old Norse sax "knife, short sword, dagger," Old High German Saxnot, name of a war-god), from Proto-Germanic *sahsam "knife," from PIE *sek- "to cut" (see section (n.)).
The word figures in the well-known story, related by Geoffrey of Monmouth, who got it from Nennius, of the treacherous slaughter by the Anglo-Saxons of their British hosts:
Accordingly they all met at the time and place appointed, and began to treat of peace; and when a fit opportunity offered for executing his villany, Hengist cried out, "Nemet oure Saxas," and the same instant seized Vortigern, and held him by his cloak. The Saxons, upon the signal given, drew their daggers, and falling upon the princes, who little suspected any such design, assassinated them to the number of four hundred and sixty barons and consuls ....The OED editors helpfully point out that the correct Old English (with an uninflected plural) would be nimað eowre seax. For other Germanic national names that may have derived from characteristic tribal weapons, cf. Frank, Lombard. As an adjective from 1560s. Still in 20c. used by Celtic speakers to mean "an Englishman" (cf. Welsh Sais, plural Seison "an Englishman;" Seisoneg "English").