source: By w?odi from Szczecin, Poland - Rock salt crystals, CC BY-SA 2.0

1. a piece of a homogeneous solid substance having a natural geometrically regular form with symmetrically arranged plane faces.

水晶

Chemistry any solid consisting of a symmetrical, ordered, three-dimensional aggregation of atoms or molecules.

〘化･鉱〙 結晶(体)

Electronics a crystalline piece of semiconductor used as an oscillator or transducer.

a clear transparent mineral, especially quartz.

a piece of crystalline substance believed to have healing powers.

水晶製品, (装飾･宝石の)水晶(玉)

2. (also crystal glass) highly transparent glass with a high refractive index:

クリスタルガラス

e.g. as modifier : a crystal chandelier.

articles made of crystal glass:

〖集合的に〗クリスタルガラスの製品［食器類］(crystal glass).

e.g. a collection of crystal.

the glass over a watch face.

｟米｠ (時計の文字盤の)ガラス

3. informal short for crystal meth (methamphetamine).

｟くだけて｠ 粉末のメタンフェタミン(crystal meth)〘覚醒剤の一種〙

clear and transparent like crystal:

水晶(製)の, 水晶質の.

e.g. the clean crystal waters of the lake.

completely transparent and unclouded.

unambiguous; easily understood:

e.g. the house rules are crystal clear.

late Old English (denoting ice or a mineral resembling it), from Old French cristal, from Latin crystallum, from Greek krustallos ‘ice, crystal’. The chemistry sense dates from the early 17th century.