Emerald

n. green precious stone

Emeralds are a variety of the mineral beryl, colored green by trace amounts of chromium and sometimes vanadium.. Beryl has a hardness of 7.5 - 8 on the 10 point Mohs scale of mineral hardness. Most emeralds are highly included, so their brittleness (resistance to breakage) is classified as generally poor. The origin of the word "emerald" is said to be a Sanskrit word meaning "green".
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Noun
1. a green transparent form of beryl; highly valued as a gemstone
(hypernym) transparent gem
2. a transparent piece of emerald that has been cut and polished and is valued as a precious gem
(hypernym) jewel, gem, precious stone
3. the green color of an emerald
(hypernym) green, greenness, viridity

n. emerald

(n.)
A precious stone of a rich green color, a variety of beryl. See Beryl.
  

(n.)
A kind of type, in size between minion and nonpare/l. It is used by English printers.
  

(a.)
Of a rich green color, like that of the emerald.