1) One explanation of this word is that it was ‘to pick, indent, or furrow the surface of stone with a narrow-pointed stone-chisel called a broach’.
In the work of Thoresby, the Yorkshire antiquary, we have exactly that definition: 1703 To broych, or broach, as Masons an Atchler, when with the small point of their ax they make it full of little pits or small holes. Perhaps that is what it meant in 1579 when it was agreed that the landstayes of Elland Bridge should be of well brooched stones, although there is little evidence that decoration in such cases was usual. In Jamieson's Etymological Dictionary of the Scottish Language, to broach was to rough hew and this is more likely to have been the meaning in the Elland context, more especially since it is was used there of the pavement, in the same sentence that the battlements were to be of well hewn stones.
2) A skewer, spit, or pointed instrument more generally.
c.1537 Item iiij or v broches of iron, with moche other stuff belonging to the kechen, Halifax
1568 Kyching stuff ... twelve broches, Healaugh Park
1614 iij pothucks ... 12 broches ... V dripping pans, Stockeld