Definition of diamond noun from the Oxford Advanced American Dictionary

      

    diamond

     noun
    noun
    NAmE//ˈdaɪmənd//
     
    , NAmE//ˈdaɪəmənd//
     
     
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  1. 1[uncountable, countable] a clear precious stone of pure carbon, the hardest substance known. Diamonds are used in jewelry and also in industry, especially for cutting glass. a ring with a diamond in it a diamond ring/necklace She was wearing her diamonds (= jewelry with diamonds in it). The lights shone like diamonds.
  2. 2[countable] a shape with four straight sides of equal length and with angles that are not right angles
  3. 3diamonds [plural] one of the four suits (= sets) in a deck of cards. The cards are marked with red diamond shapes the ten of diamonds Diamonds are trump cards in this game.
  4. 4[countable] a card of this suit You must play a diamond if you have one.
  5. 5[countable] (in baseball) the space inside the lines that connect the four bases; also used to mean the whole baseball field
  6. Idioms
    diamond in the rough
     
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    a person who has many good qualities even though they do not seem to be very polite, educated, etc.
See the Oxford Advanced Learner's Dictionary entry: diamond