Although the "steep" sense is newer, it is still true to the word's origins; arduous derives from the Latin arduus, which means "high," "steep," or "difficult."

What does the word arduous mean in the Bible?

deep, difficult to climb: difficult to accomplish: laborious.

What is the meaning of arduous in Oxford dictionary?

adjective. /ˈɑrdʒuəs/ involving a lot of effort and energy, especially over a period of time an arduous journey across the Andes The work was arduous.