means Smooth and soft to the touch, or by extension a manner, sound, or movement that glides without friction.

from From 'silk,' which traveled into English as Old English 'seoluc,' likely borrowed along the trade routes from a word also behind Latin 'sericum' and Greek 'serikos' — both pointing back to the Seres, the ancient name for the silk-producing peoples of the East. The '-y' is the plain English suffix meaning 'having the quality of,' so 'silky' is simply 'silk-like' — the thread's reputation for smoothness stretched outward to cover anything that moves with the same effortless glide.