difficult β not easily or readily done; requiring much labor, skill, or planning to be performed successfully; hard: a difficult job.
overwhelming β that overwhelms; overpowering: The temptation to despair may become overwhelming.
arduous β Something that is arduous is difficult and tiring, and involves a lot of effort.
awesome β An awesome person or thing is very impressive and often frightening.
challenging β A challenging task or job requires great effort and determination.
great β unusually or comparatively large in size or dimensions: A great fire destroyed nearly half the city.
impressive β having the ability to impress the mind; arousing admiration, awe, respect, etc.; moving; admirable: an impressive ceremony; an impressive appearance.
onerous β burdensome, oppressive, or troublesome; causing hardship: onerous duties.
powerful β physically strong, as a person: a large, powerful athlete.
tough β strong and durable; not easily broken or cut.
tremendous β extraordinarily great in size, amount, or intensity: a tremendous ocean liner; tremendous talent.
all-powerful β An all-powerful person or organization has the power to do anything they want.
colossal β If you describe something as colossal, you are emphasizing that it is very large.
effortful β marked by effort or exertion; labored.
hard β not soft; solid and firm to the touch; unyielding to pressure and impenetrable or almost impenetrable.
indomitable β that cannot be subdued or overcome, as persons, will, or courage; unconquerable: an indomitable warrior.
labored β of or relating to workers, their associations, or working conditions: labor reforms.
laboured β productive activity, especially for the sake of economic gain.
laborious β requiring much work, exertion, or perseverance: a laborious undertaking.
mammoth β any large, elephantlike mammal of the extinct genus Mammuthus, from the Pleistocene Epoch, having hairy skin and ridged molar teeth.
mighty β having, characterized by, or showing superior power or strength: mighty rulers.
murder β Law. the killing of another human being under conditions specifically covered in law. In the U.S., special statutory definitions include murder committed with malice aforethought, characterized by deliberation or premeditation or occurring during the commission of another serious crime, as robbery or arson (first-degree murder) and murder by intent but without deliberation or premeditation (second-degree murder)
overpowering β that overpowers; overwhelming: an overpowering conviction of the truth.