Source : Webster's Revised Unabridged Dictionary (1913)

Melancholy \Mel"an*chol*y\, n. [OE. melancolie, F.
   m['e]lancolie, L. melancholia, fr. Gr. ?; me`las, -anos,
   black + ? gall, bile. See {Malice}, and 1st {Gall}.]
   1. Depression of spirits; a gloomy state continuing a
      considerable time; deep dejection; gloominess. --Shak.

   2. Great and continued depression of spirits, amounting to
      mental unsoundness; melancholia.

   3. Pensive maditation; serious thoughtfulness. [Obs.] ``Hail,
      divinest Melancholy !'' --Milton.

   4. Ill nature. [Obs.] --Chaucer.

Melancholy \Mel"an*chol*y\, a.
   1. Depressed in spirits; dejected; gloomy dismal. --Shak.

   2. Producing great evil and grief; causing dejection;
      calamitous; afflictive; as, a melancholy event.

   3. Somewhat deranged in mind; having the jugment impaired.
      [Obs.] --Bp. Reynolds.

   4. Favorable to meditation; somber.

            A pretty, melancholy seat, well wooded and watered.
                                                  --Evelin.

   Syn: Gloomy; sad; dispirited; low-spirited; downhearted;
        unhappy; hypochondriac; disconsolate; heavy, doleful;
        dismal; calamitous; afflictive.

Source : WordNet®

melancholy
     adj : characterized by or causing or expressing sadness; "growing
           more melancholy every hour"; "her melancholic smile";
           "we acquainted him with the melancholy truth" [syn: {melancholic}]
     n 1: a feeling of thoughtful sadness
     2: a constitutional tendency to be gloomy and depressed
     3: a humor that was once believed to be secreted by the kidneys
        or spleen and to cause sadness and melancholy [syn: {black
        bile}]