'high-magnesium' is a compound of English 'high' and 'magnesium'. 'high' originates from Old English 'heah', where it originally meant 'tall' or 'elevated'. 'magnesium' originates from New Latin 'magnesium', named after the district 'Magnesia' in Greece and ultimately from Greek 'magnēs' meaning 'Magnesian stone'.

'magnesium' changed from Greek 'magnēs' to New Latin 'magnesia'/'magnesium' and entered modern English as 'magnesium'; 'high' changed from Old English 'heah' through Middle English to the modern form 'high'. The compound 'high-magnesium' is a modern English descriptive compound formed from these elements.

Initially, 'magnesium' referred to a mineral associated with the Magnesia region and later became the name of the chemical element 'magnesium'; 'high' originally meant 'tall' or 'elevated' and evolved into a general descriptor used in compounds to indicate a relatively large amount or degree.