Source : Webster's Revised Unabridged Dictionary (1913)

Sickness \Sick"ness\, n. [AS. se['o]cness.]
   1. The quality or state of being sick or diseased; illness;
      sisease or malady.

            I do lament the sickness of the king. --Shak.

            Trust not too much your now resistless charms;
            Those, age or sickness soon or late disarms. --Pope.

   2. Nausea; qualmishness; as, sickness of stomach.

   Syn: Illness; disease; malady. See {Illness}.

Source : WordNet®

sickness
     n 1: impairment of normal physiological function affecting part
          or all of an organism [syn: {illness}, {unwellness}, {malady}]
          [ant: {health}, {health}]
     2: the state that precedes vomiting [syn: {nausea}]