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®

unhappy
     adj 1: experiencing or marked by or causing sadness or sorrow or
            discontent; "unhappy over her departure"; "unhappy
            with her raise"; "after the argument they lapsed into
            an unhappy silence"; "had an unhappy time at school";
            "the unhappy (or sad) news"; "he looks so sad" [ant: {happy}]
     2: generalized feeling of distress [syn: {dysphoric}, {distressed}]
        [ant: {euphoric}]
     3: causing discomfort; "the unhappy truth"
     4: marked by or producing unhappiness; "infelicitous
        circumstances"; "unhappy caravans, straggling afoot
        through swamps and canebrakes"- American Guide Series
        [syn: {infelicitous}]
     [also: {unhappiest}, {unhappier}]