The Collaborative International Dictionary of English v.0.48:

Calx \Calx\, n.; pl. E. Calxes, L. Calces. [L. Calx, calcis.
   limestone; cf. Gr. ? gravel. ?, ?, pebble, Skr. ? gravel, Ir.
   carraic rock Gael. carraig, W. careg, stone. Cf. Chalk.]
   [1913 Webster]
   1. (Chem.)
      (a) Quicklime. [Obs.]
      (b) The substance which remains when a metal or mineral
          has been subjected to calcination or combustion by
          heat, and which is, or may be, reduced to a fine
          powder.
          [1913 Webster]

   Note: Metallic calxes are now called oxides.
         [1913 Webster]

   2. Broken and refuse glass, returned to the post.

WordNet (r) 3.0 (2006):

calx
    n 1: a white crystalline oxide used in the production of calcium
         hydroxide [syn: calcium oxide, quicklime, lime,
         calx, calcined lime, fluxing lime, unslaked lime,
         burnt lime]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "calx":
   ash, ashes, brand, carbon, charcoal, cinder, clinker, coal, coke,
   coom, dross, fume, lava, reek, scoria, slag, smoke, smudge, smut,
   soot, sullage