crystal

Etymology

From Middle English crystal, cristal, criȝstall, from Old English cristalla (“crystal”), a borrowing from Latin crystallum (“crystal, ice”) (later reinforced from Anglo-Norman cristall and Middle French cristal, from Latin crystallum), from Ancient Greek κρύσταλλος (krústallos, “clear ice”), from κρύος (krúos, “frost”), from Proto-Indo-European *krews- (“hard, hard outer surface, crust”).

noun

1. (countable) A solid composed of an array of atoms or molecules possessing long-range order and arranged in a pattern which is periodic in three dimensions.
2. (countable) A piece of glimmering, shining mineral resembling ice or glass.
3. (uncountable) A fine type of glassware, or the material used to make it.
4. (uncountable, slang) Crystal meth: methamphetamine hydrochloride.
   He tells me he's been shooting crystal, which I already pretty much know because he does not bother to keep his sleeves rolled down over the needle tracks. 1968, Joan Didion, “Slouching Towards Bethlehem”, in Slouching Towards Bethlehem
5. (obsolete, usually in the plural) a person's eye.
6. The glass over the dial of a watch case.

adj

1. Made of crystal.
   Its ceiling was crystal, around on the wall / Thickly studded were rubies and diamonds rare; / But purer than crystal, and brighter than all / Of the jewels adorning her glittering hall, / Was the mermaiden languishing there. 1887, Joseph W[arren] Smith, Gleanings from the Sea: Showing the Pleasures, Pains and Penalties of Life Afloat, with Contingencies Ashore, Andover, Mass.: […] the Author, page 116
   The walls were crystal, and they seemed to have hundreds of different-colored lights shifting behind them. 1985, Patricia C[ollins] Wrede, Talking to Dragons, New York, N.Y.: Tempo Books, page 146
   The uneven floor was crystal as well, as if there once had been huge crystals jutting up here, too, but ones that had been broken away and the surface crudely adzed. 2000, Dennis L[ester] McKiernan, Silver Wolf, Black Falcon, Roc Books, page 439
2. Very clear.
   "Do I make myself clear?" / "Crystal."