Having many mountains or characterized by mountainous terrain; extremely large in amount or degree.
From mountain (Old French montaigne, from Latin montanus) + suffix -ous (meaning 'full of, having the quality of'). The figurative sense of 'enormous in size or amount' developed from the literal geographical meaning in the 14th century.
The word mountainous beautifully demonstrates how geographical terms become metaphors for magnitude - we speak of mountainous debt, mountainous tasks, and mountainous evidence. This linguistic mountain-climbing from literal landscape to figurative enormity shows how humans consistently use the physical world to measure abstract concepts.
Complete word intelligence in one call. Free tier — 50 lookups/day.