The name coconut is derived from 16th century Portuguese sailors who thought the 3 small holes on the coconut shell resembled the human face so dubbed the fruit "coco" meaning "grinning face, grin, or grimace" The word nut was added in English later on.
Technically the coconut fruit is a drupe not a nut. Typical drupes include peaches, plums, and cherries.
Coconut water can be a substitute for blood plasma. The high level of sugar and other salts make it possible to add the water to the bloodstream, similar to how an IV solution works in modern medicine. Coconut water was known to be used during World War II in tropical areas for emergency transfusions.