E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Ducange derives this word from Sarah (Abrahams wife); Hottinger from the Arabic saraca (to steal); Forster from sahra (a desert); but probably it is the Arabic sharakyoun or sharkeyn (the eastern people), as opposed to Magharibë (the western peoplei.e. of Morocco). Any unbaptised person was called a Saracen in mediæval romance. (Greek, Suralknos.)
So the Arabs, or Saracens, as they are called gave men the choice of three things.E. A. Freeman: General Sketch, chap. vi. p. 117.