arduous

Needing or using up much energy; testing powers of endurance.

The movement towards a peaceful settlement has been a long and arduous political struggle.

Chelsea survived and can now turn their attentions to the Champions League final against Bayern Munich in Germany later this month as they face an increasingly arduous task to finish in the Premier League's top four.

burning; ardent

1805-1814, Dante, Henry Francis Cary (translator), The Divine Comedy Where flames the arduous Spirit of Isidore.

Difficult or exhausting to traverse.

Beyond the river, an arduous slope rises 3286 feet in 13 miles.

Mike looked up from the arduous mountain trail. They'd been climbing for five hours and he was beginning to feel irritable.