Having lost most or all of its water content; lacking moisture or fluids in the body.
From de- (remove) + hydrated (from Greek 'hydor' meaning water). Combined in the 19th century as scientists needed words for removing water from substances.
Astronauts train for spacewalks in underwater pools, and one of their biggest challenges is staying hydrated—a dehydrated astronaut in space can't sweat to cool down, which is dangerously different from Earth.
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