The Collaborative International Dictionary of English v.0.48:

Unhappy \Un*hap"py\, a.
   1. Not happy or fortunate; unfortunate; unlucky; as, affairs
      have taken an unhappy turn.
      [1913 Webster]

   2. In a degree miserable or wretched; not happy; sad;
      sorrowful; as, children render their parents unhappy by
      misconduct.
      [1913 Webster]

   3. Marked by infelicity; evil; calamitous; as, an unhappy
      day. "The unhappy morn." --Milton.
      [1913 Webster]

   4. Mischievous; wanton; wicked. [Obs.] --Shak.
      [1913 Webster] -- Un*hap"pi*ly, adv. --
      Un*hap"pi*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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