The Collaborative International Dictionary of English v.0.48:

Hyacinth \Hy"a*cinth\, n. [L. hyacinthus a kind of flower, prob.
   the iris, gladiolus, or larkspur, also a kind of gem, perh.
   the sapphire; as, a proper name, Hyacinthus, a beautiful
   Laconian youth, beloved by Apollo, fr. Gr. ?, ?: cf. F.
   hyacinthe. Cf. Jacinth. The hyacinth was fabled to have
   sprung from the blood of Hyacinthus, who was accidentally
   slain by Apollo.]
   1. (Bot.)
      (a) A bulbous plant of the genus Hyacinthus, bearing
          beautiful spikes of fragrant flowers. Hyacinthus
          orientalis is a common variety.
      (b) A plant of the genus Camassia (Camassia Farseri),
          called also Eastern camass; wild hyacinth.
      (c) The name also given to Scilla Peruviana, a
          Mediterranean plant, one variety of which produces
          white, and another blue, flowers; -- called also, from
          a mistake as to its origin, Hyacinth of Peru.
          [1913 Webster]

   2. (Min.) A red variety of zircon, sometimes used as a gem.
      See Zircon.
      [1913 Webster]

   Hyacinth bean (Bot.), a climbing leguminous plant
      (Dolichos Lablab), related to the true bean. It has dark
      purple flowers and fruit.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Zircon \Zir"con\, n. [F., the same word as jargon. See Jargon
   a variety of zircon.]
   1. (Min.) A mineral consisting predominantly of zirconium
      silicate (Zr2SiO4) occurring in tetragonal crystals,
      usually of a brown or gray color. It consists of silica
      and zirconia. A red variety, used as a gem, is called
      hyacinth. Colorless, pale-yellow or smoky-brown
      varieties from Ceylon are called jargon.
      [1913 Webster +PJC]

   2. an imitation gemstone made of cubic zirconia.
      [PJC]

   Zircon syenite, a coarse-grained syenite containing zircon
      crystals and often also elaeolite. It is largely developed
      in Southern Norway.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hyacinth
    n 1: a red transparent variety of zircon used as a gemstone
         [syn: hyacinth, jacinth]
    2: any of numerous bulbous perennial herbs