Not easy to do, achieve, or master
Requiring great or extreme bodily, mental, or spiritual strength
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It was an arduous trip.
It was an arduous climb up the mountain.
They began the arduous climb, puffing in the high elevation for ten minutes until the trail leveled and opened to their left.
It was not too arduous a task for a Sunday morning.
The job involved the most arduous of conditions with no maintenance or lubrication.