The Etymology of Layer
Layer underwent one of English's quieter but more interesting semantic shifts. It started as an agent noun: a layer was someone who lays things down, just as a player is someone who plays. Sometime in the 14th century, the meaning rotated from the person to the product — from the one doing the laying to the thing that has been laid. This agent-to-result shift appears elsewhere in English (a covering is both the act and the thing), but layer is one of the clearest examples. The deeper roots run through Old English lecgan ('to lay, place') to Proto-Germanic *lagjaną and ultimately PIE *legh- ('to lie down'). This root proved extraordinarily productive. In English alone it generated lay, lie, lair, law (originally 'something laid down'), and lees (dregs that settle). In German, the same root produced Lager ('storehouse, bed'), which gave English both lager beer (stored beer, laid down to ferment) and the grimmer compound Konzentrationslager. The geological sense — layers of rock, sediment, or soil — emerged naturally from the idea of successive surfaces laid one upon another. Computing borrowed the term for software architecture, networking models, and image editing, extending a 14th-century metaphor into digital territory without straining it at all.