What does dehydration mean?
Dehydration is the condition or process of losing too much water. In its most common sense it describes a state in which the body loses more fluid than it takes in — through heat, exercise, illness, or simply not drinking enough — resulting in thirst, dizziness, weakness, and, if untreated, more serious medical consequences. The word also has a second, technical sense: the deliberate removal of water from a substance, notably in food preservation, where dried fruits, instant soups, and powdered milk are all products of controlled dehydration. Derived from the prefix 'de-' ('removal') combined with 'hydrate' (ultimately from the Greek 'hydor', meaning water), the word entered English in the nineteenth century alongside the growth of modern physiology and chemistry. It appears frequently in medical advice, sports science, and survival guidance, usually with a cautionary tone, though in culinary contexts it can be neutral or even desirable. Related forms include the verb 'dehydrate' and the noun 'rehydration'.
Excessive loss of water from the body, causing symptoms such as thirst, weakness, and dizziness.
"The doctor diagnosed mild dehydration and advised rest and fluids."
In medical contexts, dehydration is graded as mild, moderate, or severe.
The removal of water from a substance, especially as a means of preservation.
"Dehydration is one of the oldest methods of storing food for long journeys."
Common in food science and industrial contexts.
Your body can survive weeks without food but only days without water — which is why dehydration has been a silent killer of soldiers and athletes alike throughout history.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dehydration
Dehydration was formed in English from the prefix 'de-', indicating removal or reversal, plus 'hydrate', itself built on Greek 'hydor' meaning water, which reached English through French and New Latin scientific vocabulary. The word emerged in the nineteenth century as physiology and chemistry developed precise terminology for water balance and chemical processes involving water loss. Its Greek root also gives us a family of related terms including hydrogen ('water-forming'), hydraulic, hydrology, and hydrant, all sharing the same ancient element for water.
Related word forms
How dehydration is actually used
Dehydration is used chiefly in medical, health, and scientific registers. It carries a negative connotation when applied to people and animals, implying illness or danger, but a neutral or even positive one in food science, where dehydration is a deliberate preservation technique.
Easily confused with dehydration
Desiccation refers to thorough drying out of substances (often deliberately, as in food preservation), while dehydration most often describes harmful water loss from a living body.
Rehydration is the restoration of lost fluids to the body, the remedy for dehydration rather than the condition itself.