Sickness, n.
Etymology: [AS. seócness.]
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.
Shades of meaning
Fernald has no entry of its own for sickness; he lists it under disease.
Where he writes about it:
Sickness was generally used in English speech and literature, till the close of the eighteenth century at least, for every form of physical disorder, as abundantly appears in the English Bible: "Jesus went about ... healing all manner of sickness and all manner of disease among the people," Matt. iv, 23; "Elisha was fallen sick of his sickness whereof he died," 2 Kings xiii, 14. — from disease
There is now, in England, a tendency to restrict the words sick and sickness to nausea, or "sickness at the stomach," and to hold ill and illness as the only proper words to use in a general sense. — from disease
This distinction has received but a very limited acceptance in the United States, where sick and sickness have the earlier and wider usage. — from disease
We speak of trifling ailments, a slight indisposition, a serious or a deadly disease; a slight or severe illness; a painful sickness. — from disease