'gem-adorned' is a compound formed in English from 'gem' (a noun) + the past-participle/adjectival form 'adorned' (from the verb 'adorn'). 'Gem' originates from Old French 'gemme' (from Latin 'gemma'), where 'gemma' meant 'bud' or 'jewel'; 'adorn' originates from Latin 'adornare', where the prefix 'ad-' meant 'to/toward' and 'ornare' meant 'to equip or decorate'.

The element 'gem' entered English via Old French 'gemme' (from Latin 'gemma') and became English 'gem'. 'Adorn' entered English from Latin 'adornare' through Old French/Anglo-Norman forms (e.g. Middle English 'adournen'/'adorn') and later settled as modern English 'adorn'. The compound 'gem-adorned' is a modern English formation combining these elements to mean 'decorated with gems'.

Individually, 'gem' originally referred to a jewel or bud and 'adorn' originally meant 'to equip or decorate'; combined as 'gem-adorned', the phrase has the straightforward, literal meaning 'decorated with gems', and by extension a figurative sense of being very lavishly decorated.