Bone: From skeleton to sight line

To most people, a bone is part of a skeleton: a hard, mineralized tissue that provides structure to animal bodies. It is something you might find in meat, study in anatomy class, or throw to a dog. This everyday sense has been stable for a thousand years.

In carpentry and masonry, however, to bone is a verb with a different meaning altogether. It means to sight along an object or set of objects, usually a straightedge or a line of fence posts or brickwork, in order to verify that they are level or properly aligned. A carpenter bones a line of posts by stepping back and looking along their length, the way you might squint to check if a picture frame is hanging straight. The straightedge itself, when used for this purpose, is sometimes called a boning rod or boning line. This sense depends entirely on the angle of sight, not on structure or anatomy.

The origin of this usage is a matter of practice rather than recorded etymology. One plausible account is that carpenters, having only simple tools, used actual animal bones as straightedges and sighting devices before metal tools were common. Another is that the verb simply refers to the act of making something as straight and strong as a bone. What is clear is that by the nineteenth century, boning was established jargon among builders, and it remains standard today.

The related term boneyard in industrial safety contexts carries a different metaphor. In fire management on construction or industrial sites, a boneyard is an area scraped down to bare mineral soil where smouldering material can be safely placed without igniting surrounding vegetation or debris. The name suggests barrenness, the stripped-down absence of anything combustible, much as a bone is stripped of flesh. This usage, too, exploits the bone as a symbol of exposure and reduction, but it has nothing to do with sighting or alignment.