'supremely' originates from Latin, specifically from the adjective 'supremus' (the superlative of 'superus'), where 'super-' meant 'above' or 'over'.

'supremus' passed into Old French as 'suprême' and into Middle English as 'supreme'; the modern adverb 'supremely' was formed by adding the English adverbial suffix '-ly' to 'supreme'.

Initially it meant 'highest, uppermost', and over time it came to be used more broadly as 'to the highest degree' or 'extremely' in modern usage.