c. 1300, 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 "silken; pertaining to the Seres," an oriental people of Asia from whom the Greeks got silks. 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 in Greek might be a rendering via Mongolian of the Chinese word for "silk," but this is uncertain.
Also found in Old Norse as silki but not elsewhere in Germanic. The more common Germanic form is represented by Middle English say, from Old French seie, with Spanish seda, Italian seta, Dutch zijde, German Seide is from Medieval Latin seta "silk," 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). Figurative use of silk-stocking (n.) is from 1590s; as an adjective meaning "wealthy" it is attested from 1798, American English (silk stockings, especially worn by men, being regarded as extravagant and reprehensible, indicative of luxurious habits). Silk-screen (n.) is first attested 1930; as a verb from 1961. Silk road so called in English from 1931.