Source : Webster's Revised Unabridged Dictionary (1913)

Unhappy \Un*hap"py\, a.
   1. Not happy or fortunate; unfortunate; unlucky; as, affairs
      have taken an unhappy turn.

   2. In a degree miserable or wretched; not happy; sad;
      sorrowful; as, children render their parents unhappy by
      misconduct.

   3. Marked by infelicity; evil; calamitous; as, an unhappy
      day. ``The unhappy morn.'' --Milton.

   4. Mischievous; wanton; wicked. [Obs.] --Shak. --
      {Un*hap"pi*ly}, adv. -- {Un*hap"pi*ness}, n.

Source : WordNet®

unhappiness
     n 1: emotions experienced when not in a state of well-being [syn:
           {sadness}] [ant: {happiness}]
     2: state characterized by emotions ranging from mild
        discontentment to deep grief [ant: {happiness}]