1. [n]  the baseball playing field
2. [n]  the area of a baseball field that is enclosed by 3 bases and home plate
3. [n]  a playing card in the minor suit of diamonds
4. [n]  a transparent piece of diamond that has been cut and polished and is valued as a precious gem
5. [n]  very hard native crystalline carbon valued as a gem

Diamond
Matthew Hart, editor of Rapaport Diamond Report, explores the dynamics of the diamond trade in all of its mystery, mastery, and malfeasance.

more details ...

1. \Di"a*mond\ (?; 277), n. [OE. diamaund, diamaunt, F.
   diamant, corrupted, fr. L. adamas, the hardest iron, steel,
   diamond, Gr. ?. Perh. the corruption is due to the influence
   of Gr. ? transparent. See {Adamant}, {Tame}.]
   1. A precious stone or gem excelling in brilliancy and
      beautiful play of prismatic colors, and remarkable for
      extreme hardness.
   Note: The diamond is native carbon in isometric crystals,
         often octahedrons with rounded edges. It is usually
         colorless, but some are yellow, green, blue, and even
         black. It is the hardest substance known. The diamond
         as found in nature (called a rough diamond) is cut, for
         use in jewelry, into various forms with many reflecting
         faces, or facets, by which its brilliancy is much
         increased. See {Brilliant}, {Rose}. Diamonds are said
         to be of the first water when very transparent, and of
         the second or third water as the transparency
         decreases.
   2. A geometrical figure, consisting of four equal straight
      lines, and having two of the interior angles acute and two
      obtuse; a rhombus; a lozenge.
   3. One of a suit of playing cards, stamped with the figure of
      a diamond.
   4. (Arch.) A pointed projection, like a four-sided pyramid,
      used for ornament in lines or groups.
   5. (Baseball) The infield; the square space, 90 feet on a
      side, having the bases at its angles.
   6. (Print.) The smallest kind of type in English printing,
      except that called brilliant, which is seldom seen.
   Note: [hand] This line is printed in the type called
         {Diamond}.
   {Black diamond}, coal; (Min.) See {Carbonado}.
   {Bristol diamond}. See {Bristol stone}, under {Bristol}.
   {Diamond beetle} (Zo["o]l.), a large South American weevil
      ({Entimus imperialis}), remarkable for its splendid luster
      and colors, due to minute brilliant scales.
   {Diamond bird} (Zo["o]l.), a small Australian bird
      ({Pardalotus punctatus}, family {Ampelid[ae]}.). It is
      black, with white spots.
   {Diamond drill} (Engin.), a rod or tube the end of which is
      set with black diamonds; -- used for perforating hard
      substances, esp. for boring in rock.
   {Diamond finch} (Zo["o]l.), a small Australian sparrow, often
      kept in a cage. Its sides are black, with conspicuous
      white spots, and the rump is bright carmine.
   {Diamond groove} (Iron Working), a groove of V-section in a
      roll.
   {Diamond mortar} (Chem.), a small steel mortar used for
      pulverizing hard substances.
   {Diamond-point tool}, a cutting tool whose point is
      diamond-shaped.
   {Diamond snake} (Zo["o]l.), a harmless snake of Australia
      ({Morelia spilotes}); the carpet snake.
   {Glazier's diamond}, a small diamond set in a glazier's tool,
      for cutting glass.
   

2. \Di"a*mond\ (?; 277), a.
   Resembling a diamond; made of, or abounding in, diamonds; as,
   a diamond chain; a diamond field.
   

One of five pedagogical languages based on Markov algorithms, used in "Nonpareil, a Machine Level Machine Independent Language for the Study of Semantics", B. Higman, ULICS Intl Report No ICSI 170, U London (1968). (cf. Brilliant, Nonpareil, Pearl[3], Ruby[2]).

(1.) A precious gem (Heb. yahalom', in allusion to its hardness), otherwise unknown, the sixth, i.e., the third in the second row, in the breastplate of the high priest, with the name of Naphtali engraven on it (Ex. 28:18; 39:11; R.V. marg., "sardonyx.")

(2.) A precious stone (Heb. shamir', a sharp point) mentioned in Jer. 17:1. From its hardness it was used for cutting and perforating other minerals. It is rendered "adamant" (q.v.) in Ezek. 3:9, Zech. 7:12. It is the hardest and most valuable of precious stones.