Synonyms for Arduousness:

n.

•arduousness (noun)
strenuousness.
•attribute (noun)
strenuousness.
•difficulty (noun)
difficulty, fussiness, contrariness, cumbersomeness, painfulness, onerousness, complexity, knottiness, tightness, harshness, complication, toughness, stressfulness, adversity, wearying, roughness, ordeal, wearisomeness, ticklishness, hardness, strenuousness, cantankerousness, trickiness, formidability.
•painfulness (noun)
distressfulness, hurtfulness, unpleasantness, agony, odiousness, grievousness, irritation, torment, painfulness, annoyingness, oppressiveness, woefulness, anguish, aggravation, severity, torture, cruelty, soreness, bitterness, ache, offensiveness, misery, uncomfortableness, acuteness, irksomeness.

Other synonyms:

•n.
difficulty.