1. a pure or nearly pure, extremely hard form of carbon, naturally crystallized in the isometric system.
  2. a piece of this stone.
  3. a transparent, flawless or almost flawless piece of this stone, especially when cut and polished, valued as a precious gem.
  4. a ring or other piece of jewelry containing such a precious stone, especially an engagement ring.
  5. a piece of this stone used in a drill or cutting tool.
  6. a tool provided with such an uncut stone, used for cutting glass.
  7. crystallized carbon, or a piece of it, artificially produced.
  8. an equilateral quadrilateral, especially as placed with its diagonals vertical and horizontal; a lozenge or rhombus.
  9. any rhombus-shaped figure or object oriented with its diagonals vertical and horizontal.
  10. a red rhombus-shaped figure on a playing card.
  11. a card of the suit bearing such figures.
  12. diamonds, (used with a singular or plural verb) the suit so marked: Diamonds is trump. Diamonds are trump.
  13. Baseball.
    1. the space enclosed by home plate and the three bases; infield.
    2. the entire playing field.
  14. Printing. a 4½-point type of a size between brilliant and pearl.


  1. made of or set with a diamond or diamonds.
  2. having the shape of a diamond: a dress with a diamond print.
  3. indicating the 75th, or sometimes the 60th, event of a series, as a wedding anniversary.

verb (used with object)

  1. to adorn with or as if with diamonds.

  1. diamond in the rough, a person of fine character but lacking refined manners or graces.


  1. Neil,born 1941, U.S. singer and songwriter.
  2. Cape, a hill in Canada, in S Quebec, on the St. Lawrence River.


    1. a colourless exceptionally hard mineral (but often tinted yellow, orange, blue, brown, or black by impurities), found in certain igneous rocks (esp the kimberlites of South Africa). It is used as a gemstone, as an abrasive, and on the working edges of cutting tools. Composition: carbon. Formula: C. Crystal structure: cubic
    2. (as modifier)a diamond ring Related adjective: diamantine
  1. geometry
    1. a figure having four sides of equal length forming two acute angles and two obtuse angles; rhombus
    2. (modifier)rhombic
    1. a red lozenge-shaped symbol on a playing card
    2. a card with one or more of these symbols or (when plural) the suit of cards so marked
  2. baseball
    1. the whole playing field
    2. the square formed by the four bases
  3. (formerly) a size of printer’s type approximately equal to 4 1/2 point
  4. black diamond a figurative name for coal
  5. rough diamond
    1. an unpolished diamond
    2. a person of fine character who lacks refinement and polish


  1. (tr) to decorate with or as with diamonds

early 14c., from Old French diamant, from Medieval Latin diamantem (nominative diamas), from Vulgar Latin *adiamantem (altered by influence of the many Greek words in dia-), from Latin adamantem (nominative adamans) “the hardest metal,” later, “diamond” (see adamant). Playing card suit is from 1590s; Sense in baseball is American English, 1875.

  1. A form of pure carbon that occurs naturally as a clear, cubic crystal and is the hardest of all known minerals. It often occurs as octahedrons with rounded edges and curved surfaces. Diamond forms under conditions of extreme temperature and pressure and is most commonly found in volcanic breccias and in alluvial deposits. Poorly formed diamonds are used in abrasives and in industrial cutting tools.
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