means A hollow fitting designed to receive and hold something — a plug, a bone, an eyeball, a light bulb — so the two parts lock together.

from From Anglo-Norman 'soket,' a diminutive of Old French 'soc,' meaning a ploughshare — the metal point of a plough. The likely image is of a small ploughshare-shaped spike or its hollow fitting; over time the word drifted from the blade to the socket that received it. The 'soc' itself is thought to be of Gaulish or Celtic origin, related to words for a pig's snout, since a ploughshare roots through earth the way a snout does.