The Rumanau people derived their name from two words "ru" and "ranah". The word ru is equivalent to the English phrase "to be with" or "to work with", and ranah refers to "wet earth" or "muddy soil". Thus the named Rumanau people means people who work with muddy soil. Wet paddy cultivation is the only known occupation among Kadazan-Dusun which involves "working with muddy soil". The Rumanau were the first ethnic group migrating out from Nunuk Ragang to acquire the skill of wet paddy cultivation. The paddy cultivation phase in Momolianism evolution had a big impact on the Rumanau people.