arduous

Adjective

arduous (comparative more arduous, superlative most arduous)

1. Needing or using up much energy; testing powers of endurance.
   • The movement towards a peaceful settlement has been a long and arduous political struggle.
   • The slave-labour camps proliferated and became an important factor in the state economy, especially in regions where conditions were most arduous, as in the mines and forests of Siberia.1978 [1976], Leszek Kołakowski, translated by P[aul] S[teven] Falla, Main Currents of Marxism, volume III: The Breakdown, Oxford: Clarendon Press, translation of Główne nurty marksizmu: rozkład (in...
2. (obsolete) burning; ardent
   • Where flames the arduous Spirit of Isidore.1805-1814, Dante, Henry Francis Cary (translator), The Divine Comedy
3. Difficult or exhausting to traverse.
   • Beyond the river, an arduous slope rises 3286 feet in 13 miles.1974, Sue Bowder, The American biking atlas & touring guide, page 77
   • Mike looked up from the arduous mountain trail. They'd been climbing for five hours and he was beginning to feel irritable.1999, Scott Ciencin, Mike Fredericks, Dinoverse