calx

Etymology

From Latin calx (“lime”). Doublet of cauk and chalk.

noun

1. (now chiefly historical) The substance which remains after a metal or mineral has been thoroughly burnt, once seen as being the essential substance left after the expulsion of phlogiston, but now recognised as being the metallic oxide (or, in some cases, the metal in a state of sublimation).
   The regeneration of mercury from its calx, without addition of any other substance, had been a chief example for anti-phlogiston, but that could, as Kirwan showed, be explained in a way consistent with phlogiston theory. 2004, Robert E Schofield, The Enlightened Joseph Priestley, Pennsylvania State University, page 179
2. In the Eton College wall game, an area at the end of the field where a shy can be scored by lifting the ball against the wall with one's foot.