Source : Webster's Revised Unabridged Dictionary (1913)

Heavy \Heav"y\, a. [Compar. {Heavier}; superl. {Heaviest}.] [OE.
   hevi, AS. hefig, fr. hebban to lift, heave; akin to OHG.
   hebig, hevig, Icel. h["o]figr, h["o]fugr. See {Heave}.]
   1. Heaved or lifted with labor; not light; weighty;
      ponderous; as, a heavy stone; hence, sometimes, large in
      extent, quantity, or effects; as, a heavy fall of rain or
      snow; a heavy failure; heavy business transactions, etc.;
      often implying strength; as, a heavy barrier; also,
      difficult to move; as, a heavy draught.

   2. Not easy to bear; burdensome; oppressive; hard to endure
      or accomplish; hence, grievous, afflictive; as, heavy
      yokes, expenses, undertakings, trials, news, etc.

            The hand of the Lord was heavy upon them of Ashdod.
                                                  --1 Sam. v. 6.

            The king himself hath a heavy reckoning to make.
                                                  --Shak.

            Sent hither to impart the heavy news. --Wordsworth.

            Trust him not in matter of heavy consequence.
                                                  --Shak.

   3. Laden with that which is weighty; encumbered; burdened;
      bowed down, either with an actual burden, or with care,
      grief, pain, disappointment.

            The heavy [sorrowing] nobles all in council were.
                                                  --Chapman.

            A light wife doth make a heavy husband. --Shak.

   4. Slow; sluggish; inactive; or lifeless, dull, inanimate,
      stupid; as, a heavy gait, looks, manners, style, and the
      like; a heavy writer or book.

            Whilst the heavy plowman snores.      --Shak.

            Of a heavy, dull, degenerate mind.    --Dryden.

            Neither [is] his ear heavy, that it can not hear.
                                                  --Is. lix. 1.

   5. Strong; violent; forcible; as, a heavy sea, storm,
      cannonade, and the like.

   6. Loud; deep; -- said of sound; as, heavy thunder.

            But, hark! that heavy sound breaks in once more.
                                                  --Byron.

   7. Dark with clouds, or ready to rain; gloomy; -- said of the
      sky.

   8. Impeding motion; cloggy; clayey; -- said of earth; as, a
      heavy road, soil, and the like.

   9. Not raised or made light; as, heavy bread.

   10. Not agreeable to, or suitable for, the stomach; not
       easily digested; -- said of food.

   11. Having much body or strength; -- said of wines, or other
       liquors.

   12. With child; pregnant. [R.]

   {Heavy artillery}. (Mil.)
       (a) Guns of great weight or large caliber, esp. siege,
           garrison, and seacoast guns.
       (b) Troops which serve heavy guns.

   {Heavy cavalry}. See under {Cavalry}.

   {Heavy fire} (Mil.), a continuous or destructive cannonading,
      or discharge of small arms.

   {Heavy metal} (Mil.), large guns carrying balls of a large
      size; also, large balls for such guns.

Source : WordNet®

heavy metal
     n 1: a metal of relatively high density (specific gravity greater
          than about 5) or of high relative atomic weight
     2: loud and harsh sounding rock music with a strong beat;
        lyrics usually involve violent or fantastic imagery

Source : Free On-Line Dictionary of Computing

heavy metal
     
        {big iron}