"fine soft thread produced by the larvae of certain types of moths, feeding on mulberry leaves;" c. 1300, silke, from Old English seoloc, sioloc "silk, silken cloth," from Latin sericum "silk," plural serica "silken garments, silks," literally "Seric stuff," neuter of Sericus, from Greek Serikos "pertaining to the Sēres," an oriental people of Asia from whom the Greeks got silks. Their region is vaguely described but seems to correspond to northern China as approached from the northwest.
Western cultivation began 552 C.E., when agents from Byzantium impersonating monks smuggled silkworms and mulberry leaves out of China. Chinese si "silk," Manchurian sirghe, Mongolian sirkek have been compared to this and the people-name Seres in Greek might be a rendering via Mongolian of the Chinese word for "silk," but this is uncertain.
Cognate with Old Norse silki but the word is not found elsewhere in Germanic. The more common Germanic form is represented by Middle English say, from Old French seie, which, with Spanish seda, Italian seta, Dutch zijde, and German Seide, is from Medieval Latin seta "silk," which is perhaps elliptical for seta serica, or else a particular use of seta "bristle, hair" (see seta (n.)).
According to some sources [Buck, OED], the use of -l- instead of -r- in the Balto-Slavic form of the word (Old Church Slavonic šelku, Lithuanian šilkai) passed into English via the Baltic trade and may reflect a Chinese dialectal form, or a Slavic alteration of the Greek word. But the Slavic linguist Vasmer dismisses that, based on the initial sh- in the Slavic words, and suggests the Slavic words are from Scandinavian rather than the reverse.
As an adjective from mid-14c. In reference to the "hair" of corn, 1660s, American English (corn-silk is from 1861). The ancient Silk Road was so called in English by 1895.