'gradually' originates from Latin, specifically the word 'gradualis,' where 'gradus' meant 'step.' 'Declining' originates from Latin, specifically the word 'declinare,' where 'de-' meant 'down' and 'clinare' meant 'to lean.'

'gradualis' transformed into the French word 'graduel,' and eventually became the modern English word 'gradual.' 'Declinare' transformed into the French word 'décliner,' and eventually became the modern English word 'decline.'

Initially, 'gradual' meant 'by steps,' and 'decline' meant 'to bend down.' Over time, they evolved into their current meanings of 'slowly' and 'decrease,' respectively.