anxiety

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A state of uneasiness and apprehension, as about future uncertainties.
• noun A cause of anxiety.
• noun Psychiatry A state of apprehension, uncertainty, and fear resulting from the anticipation of a realistic or fantasized threatening event or situation, often impairing physical and psychological functioning.
• noun Eager, often agitated desire.

from The Century Dictionary.

• noun The apprehension caused by danger, misfortune, or error; concern or solicitude respecting some event, future or uncertain; disturbance, uneasiness of mind, or care, occasioned by trouble.
• noun In pathology, a state of restlessness and agitation, with general indisposition, and a distressing sense of oppression at the epigastrium.

from the GNU version of the Collaborative International Dictionary of English.

• noun Concern or solicitude respecting some thing or event, future or uncertain, which disturbs the mind, and keeps it in a state of painful uneasiness.
• noun Eager desire.
• noun (Med.) A state of restlessness and agitation, often with general indisposition and a distressing sense of oppression at the epigastrium.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An unpleasant state of mental uneasiness, nervousness, apprehension and obsession or concern about some uncertain event.
• noun An uneasy or distressing desire (for something).
• noun pathology A state of restlessness and agitation, often accompanied by a distressing sense of oppression or tightness in the stomach.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a vague unpleasant emotion that is experienced in anticipation of some (usually ill-defined) misfortune
• noun (psychiatry) a relatively permanent state of worry and nervousness occurring in a variety of mental disorders, usually accompanied by compulsive behavior or attacks of panic