'gradually' originates from Latin, specifically the word 'gradualis,' where 'gradus' meant 'step.' 'Increase' originates from Latin, specifically the word 'increscere,' where 'in-' meant 'into' and 'crescere' meant 'to grow.'

'gradualis' transformed into the French word 'graduel,' and eventually became the modern English word 'gradual.' 'Increscere' transformed into the French word 'croistre,' and eventually became the modern English word 'increase.'

Initially, 'gradual' meant 'by steps,' and 'increase' meant 'to grow into something.' Over time, 'gradually-increased' evolved to describe a slow and steady rise.