'supplementarily' originates from Latin, specifically the word 'supplementum,' where 'supple-' meant 'to fill up' and '-mentum' meant 'instrument or means.'

'supplementum' transformed into the French word 'supplémentaire,' and eventually became the modern English word 'supplementary' through Middle English.

Initially, it meant 'to fill up or complete,' but over time it evolved into its current meaning of 'additional or extra.'