c. 1300, sauns, saun, "without" (mid-12c. in surnames), from Old French san, sans, sen, senz (some of the forms with adverbial genitive -s) "without, except, apart, not counting." This is cognate with Provençal senes, Old Catalan senes, Old Spanish sen (Spanish sin), Old Italian sen, all from Vulgar Latin *sene, from Latin sine "without," an enlarged form of sed, se "without" (from PIE root *sen(e)- "apart, separated;" see sunder).
"A French word which has existed long in English without becoming naturalized; now archaic or affected, except as used in heraldry ..." [Century Dictionary, 1891]; OED writes that the words limited modern use is "chiefly with reminiscence of Shakespere," which it spells that way. In reference to fonts, by 1927, short for sans-serif. Sans souci, French, as an adverbial phrase "free from care, without care or concern," was the name of Frederick the Great's royal palace at Potsdam.