'decreasable' originates from the English word 'decrease,' which comes from the Old French word 'decreistre,' derived from the Latin 'decrescere,' where 'de-' meant 'down' and 'crescere' meant 'to grow.'

'decrescere' transformed into the Old French word 'decreistre,' and eventually became the modern English word 'decrease' through Middle English.

Initially, it meant 'to grow down or diminish,' and this meaning has largely remained the same in modern usage.