Arduous means requiring tremendous effort, energy, or perseverance. When a task is arduous, it's physically exhausting, mentally draining, or both. Climbing a steep mountain trail with a heavy backpack is arduous. Working through a complex math problem that takes an hour of concentrated thinking is arduous. Training for months to run a marathon is arduous.

The word captures difficulty that tests your limits and demands sustained effort over time. A single difficult math problem might be challenging, but a three-hour exam covering an entire year's worth of material feels truly arduous. Digging a garden bed in rocky soil for an afternoon, or practicing piano scales until your fingers ache, are arduous efforts.

Notice that arduous doesn't mean impossible. It describes tasks that can be done but require real grit and determination. When you finally complete something arduous, whether it's finishing a tough book report or helping your family move furniture all day, you've earned a genuine sense of accomplishment. The difficulty is what makes the achievement meaningful.