Dehydration

n. drying up; loss of water; abnormal lack of water in the body due to insufficient intake of liquids or extreme loss of fluids by sweating or vomiting or due to diarrhea (Medicine); lack of water; removal of water, removal of moisture

Dehydration (hypohydration) is the removal of water (hydro in ancient Greek) from an object. Medically, it is a condition in which the body contains an insufficient volume of water for normal functioning.
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(n.)
The act or process of freeing from water; also, the condition of a body from which the water has been removed.
  

Excessive loss of body water. Diseases of the gastrointestinal tract may lead to dehydration. One clue to dehydration is a rapid drop in weight. A loss of over 10% (15 pounds in a person weighing 150 pounds) is considered severe. Symptoms include increasing thirst, dry mouth, weakness or lightheadedness (particularly if worsening on standing), or a darkening/decrease in urination are suggestive. Severe dehydration can lead to changes in the body’s chemistry, kidney failure, and become life-threatening. The best way to treat dehydration is to prevent it from occurring. If one suspects fluid loss is excessive, notify a physician. Intravenous or oral fluid replacement may be needed.

A condition caused by the loss of too much water from the body. Severe diarrhea or vomiting can cause dehydration.