Q From Martin Crowe: Why is road metal called metal?
A We use metal these days in a specific technical sense, one that’s hard to define simply, but which we recognise when we see it. The New Oxford Dictionary of English, for example, defines it as “a solid material which is typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivity”.
The original sense was much broader. The English word comes from Latin metallum, a mine or quarry. So a metal was anything useful that had been extracted from the ground. Since most of the substances men searched for were what we now call metals (gold, silver, tin, copper, and the like), the shift of sense is easy to understand. Another shift of sense, to a figurative one, plus a change of spelling, gave us mettle.
But the old sense survived for another class of substances that were likewise extracted from the ground. Historically, these have included sand, clay, rock and earthen matter in general. Near the end of the eighteenth century, the word started to be used in particular for the crushed rock that formed part of the system of building a sealed and waterproof road surface pioneered by the Scots engineer John McAdam. It’s from that specific use of the word that the term road metal derives.