Staple: fastener or mine shaft?

To most people, a staple is a U-shaped piece of wire, driven through paper or fabric to hold sheets together. The word comes from the Old English stapol, meaning post or pillar, which makes sense: it stands upright and bears weight. The fastener is named for that posture.

In mining, a staple is a shaft that serves the same metaphorical purpose as a paper fastener serves for documents: it joins separate layers and holds them in relationship. Specifically, a staple shaft runs vertically or nearly so between two or more working levels of a mine, allowing workers and materials to move between them. It is smaller and shorter than the main shaft that descends from surface to the deepest level. Where the main shaft may be hundreds of metres deep, a staple connects adjacent or nearby levels that are already many metres below ground.

The staple is essential to mine layout. Once a shaft reaches depth and the miners have begun extracting ore or coal horizontally at different levels, a staple provides access that does not require a long journey back to the main shaft. A miner working at one level can climb or be lowered into the staple to reach another working level without returning to surface. Ventilation air and water drainage also use staple shafts.

The word transferred to mining because both the fastener and the mine shaft perform a binding function: they connect separate things and hold them together in a system. The mining sense is old; it appears in technical writing by the 18th century. Mining came before the modern office staple (which was patented in the 19th century), so the fastener may have borrowed the term from mining, not the reverse.