1. characterized by effort to the point of exhaustion; especially physical effort

- worked their arduous way up the mining valley

- hard labor

Similar word(s): effortful, backbreaking, grueling, gruelling, hard, heavy, laborious, operose, punishing, toilsome

2. taxing to the utmost; testing powers of endurance

- your willingness after these six arduous days to remain here

Similar word(s): effortful, straining, strenuous

3. difficult to accomplish; demanding considerable mental effort and skill

- the arduous work of preparing a dictionary

Similar word(s): difficult, hard

Sentences with arduous as an adjective:

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

- Where flames the arduous Spirit of Isidore. — Cary.