Middle English Saracene, Sarcene, Sarazyn, Sarasine, "a Turk; an Arab; a Muslim," from Old English (in translations from Latin), from Old French Saracin, Sarrasine or Medieval Latin Saracenus, from Greek sarakenos. This usually is said to be from Arabic sharquiyin, accusative plural of sharqiy "eastern," from sharq "east, sunrise," but this is not certain. In medieval times the name was associated with that of Biblical Sarah (q.v.).
Peple þat cleped hem self Saracenys, as þogh þey were i-come of Sarra [Ranulph Higden’s "Polychronicon," mid-14c., John Trevisa's translation, 1380s ]
It was the name Greeks and Romans gave to the nomads of the Syrian and Arabian deserts and the inhabitants of Arabia Felix, in the West it took on a sense of "Middle Eastern Muslim" from the Crusades. It also could be applied to any non-Christian people against whom a crusade was preached (the pagan Lithuanians), and in Middle English it was used generally for "one who is not a Christian or Jew; heathen, pagan" (mid-13c.). From c. 1300 as an adjective. Related: Saracenic; Sarcenism ("Islam"), and compare sarsen. Sarsinrie, "the Saracen people or country," is attested in mid-15c.