arduous

adjective3

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.
2. •
   Difficult or exhausting to traverse.

   • Beyond the river, an arduous slope rises 3286 feet in 13 miles. — 1974
3. •
   (no longer used) burning; ardent

   • Where flames the arduous Spirit of Isidore. — 1805