"smooth, lustrous silken cloth; silk fabric with a very glossy surface and the back less so," mid-14c., from Old French satin (14c.), perhaps from Arabic (atlas) zaytuni, literally "(satin) from Zaitun," name of a place in China, perhaps modern Quanzhou in Fukien province, a major port in the Middle Ages with a resident community of European traders.
On this theory the form of the word was influenced in French by Latin seta "silk." OED finds the Arabic connection etymologically untenable and takes the French word as being from Latin seta via a Late Latin or Vulgar Latin *pannus setinus "silken cloth."
As an adjective from mid-15c., "made of silk." By c. 1600 as "clothed in satin;" by 1826 as "resembling satin."