Magnesium

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From New Latin magnēsium, from Ancient Greek μαγνησία(magnēsía), after Μαγνησία(Magnēsía, “ Magnesia”), a region in Thessaly. Coined by British chemist Humphry Davy, as a modification of his original suggestion, magnium.

etymonline

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magnesium (n.)

silvery-white metallic element, 1808, coined by English chemist Sir Humphry Davy from the white alkaline earth magnesia (q.v.), in which it was found. With metallic element ending -ium.