'declivous' originates from Latin, specifically the word 'declivis,' where 'de-' meant 'down' and 'clivus' meant 'slope.'

'declivis' transformed into the Medieval Latin word 'declivus,' and eventually became the modern English word 'declivous.'

Initially, it meant 'downward slope,' but over time it evolved into its current meaning of 'sloping downward or inclined.'