Synonyms for Grueling:

adj.

•difficult, taxing (adjective)
crushing, backbreaking, trying, punishing, hard, arduous, laborious, heavy, severe, excruciating, Fatiguing, tiring.
•painful (adjective)
bothersome, cutting, distressful, sore, Gnawing, arduous, painful, burdensome, Cramping, disagreeable, offensive, annoying, harrowing, Torturing., irritating, oppressive, horrendous, smarting, piercing, acute, unpleasant, severe, stabbing, trying, hurtful, chafing, woeful, stinging, troublesome, insufferable, Irksome, withering, crushing, inflaming, bitter, tormenting, agonizing, uncomfortable, odious, throbbing, aggravating, anguishing, aching, grievous, unbearable, cruel, biting, excruciating, Besetting, miserable, wrenching.

n.

be an effort, complicated. •exhausting (noun)
Fatiguing, tiring.
•grueling (noun)
backbreaking, punishing, labourious, gruelling, effortful, arduous, hard, toilsome, heavy, laborious.

Other synonyms:

•Other relevant words:
gruelling, tiring, heavy, toilsome, backbreaking, labourious, Fatiguing, punishing, hard, effortful, laborious.