The English word socket arrived in the 13th century from Anglo-Norman soket, a diminutive form of Old French soc, meaning plowshare. The Old French word was borrowed from Gaulish *succos, a Celtic word meaning plowshare and also pig's snout — the metal blade that cuts through earth was likened to a pig rooting in the soil. The Gaulish word is cognate with Welsh swch (plowshare) and Irish Gaelic soc (plowshare, snout), all deriving from the Celtic branch of Indo-European. Some etymologists have connected the Celtic root to PIE *sū- (pig), suggesting that the agricultural implement was named for the animal whose digging behavior it imitated.
The diminutive soket in Anglo-Norman originally referred to the hollow iron head of a spear, lance, or arrow — the cup-shaped fitting into which the wooden shaft was inserted. This iron fitting resembled a small plowshare in shape, which explains the diminutive derivation: a soket was a little soc. The word thus began its English life as a specific term from medieval weaponry and military equipment.
From this initial sense of a hollow receptacle for a shaft, socket generalized during the 14th and 15th centuries to denote any cavity or hollow into which something fits. By the 15th century, eye socket was in use to describe the bony cavity of the skull that houses the eyeball (the anatomical term is orbit, from Latin orbita, but socket remains the common English word). Candlestick sockets, joint sockets in anatomy, and tool sockets in carpentry all followed the same semantic pattern: a hollow designed to receive an insert.
The word gained new applications with the development of electrical technology in the late 19th and early 20th centuries. An electrical socket (or outlet) is a wall-mounted receptacle into which a plug is inserted to establish an electrical connection. A light socket (or lamp holder) is the threaded or bayonet-type fitting into which a light bulb is screwed or pushed. These usages, which are now among the most common applications of the word, represent a natural extension of the medieval concept of a hollow receiving a fitted object.
In computing, socket acquired a technical meaning in the 1980s with the development of network programming. A network socket is an endpoint in a communication flow between two programs running over a network. The Berkeley sockets API, developed at the University of California, Berkeley, in the early 1980s for the BSD Unix operating system, became the standard interface for network programming and gave the word socket its computing sense. The metaphor is the same: a socket is a point of connection where something
The Celtic origin of socket makes it one of the relatively small number of English words that trace back to Gaulish, the Celtic language of pre-Roman and Roman-era Gaul (modern France). Most Gaulish words in English arrived through French, which absorbed a substrate of Celtic vocabulary before and during the Roman conquest of Gaul. Other English words with probable Gaulish origins include car (from Gaulish *karros, a wheeled vehicle), breeches (possibly from Gaulish *brāca), and ambassador (through a complex chain involving Gaulish *ambactos, a servant or dependent).
The phonological development from soc to soket to socket is straightforward: the Anglo-Norman diminutive suffix -et was added to soc to produce soket, and the word was adopted into English with minimal change. The spelling with ck reflects the standard English representation of the /k/ sound after a short vowel.
Socket's journey from a Celtic pig's snout, through a Roman-era plowshare, to a medieval spearhead fitting, and finally to the electrical outlet on a modern wall, traces a remarkable chain of metaphorical extensions spanning two thousand years and multiple technologies.