arduous

The word arduous originates from the Latin adjective arduus, which literally meant "high, lofty, or steep," as in a difficult mountain to climb. This Latin term is thought to derive from the Proto-Indo-European root h₃erdʰ- ("to grow, high"), connecting the physical concept of height to metaphorical difficulty. Over time, the primary sense shifted from the literal steepness of a slope to the figurative sense of any task requiring great and sustained exertion. Thus, the modern abstract meaning of "extremely difficult and demanding" retains the core logic of its ancient root: overcoming a steep challenge.

Structure: ardu (steep, difficult) + ous (adjective suffix) - ardu: From Latin arduus meaning "high, steep, difficult." - ous: A suffix of Latin origin (-osus) used to form adjectives meaning "full of, characterized by, or having the qualities of."