Meaning

adjective characterized by effort to the point of exhaustion; especially physical effort

adjective taxing to the utmost; testing powers of endurance; ; ; - F.D.Roosevelt

adjective difficult to accomplish; demanding considerable mental effort and skill

originEtymology tree Latin arduus English arduous From Latin arduus (“lofty, high, steep, hard to reach, difficult, laborious”), akin to Irish ard (“high”).

Etymology from Wiktionary, CC BY-SA 3.0