shockingly brutal or cruel; "murder is an atrocious crime"; "a grievous offense against morality"; "a grievous crime"; "no excess was too monstrous for them to commit"
If you describe a situation or event as monstrous, you mean that it is extremely shocking or unfair. She endured the monstrous behaviour for years = atrocious + monstrously mon·strous·ly Your husband's family has behaved monstrously
emphasis If you describe an unpleasant thing as monstrous, you mean that it is extremely large in size or extent. a monstrous copper edifice + monstrously mon·strous·ly It would be monstrously unfair = hugely
If you describe something as monstrous, you mean that it is extremely frightening because it appears unnatural or ugly. the film's monstrous fantasy figure. = hideous