arduous

As adjectives the difference between arduous and relentless

is that arduous is needing or using up much energy; testing powers of endurance while relentless is unrelenting or unyielding in severity.

As adjectives the difference between formidable and arduous

is that formidable is causing fear, dread, awe or admiration as a result of size, strength, or some other impressive quality; commanding respect; causing wonder or astonishment while arduous is needing or using up much energy; testing powers of endurance.

As adjectives the difference between stiff and arduous

is that stiff is of an object, rigid, hard to bend, inflexible while arduous is needing or using up much energy; testing powers of endurance.

As a noun stiff

is an average person, usually male, of no particular distinction, skill, or education, often a working stiff''''' or ''lucky '''stiff .

As a verb stiff

is to fail to pay that which one owes (implicitly or explicitly) to another, especially by departing hastily.

As adjectives the difference between arduous and exigent

is that arduous is needing or using up much energy; testing powers of endurance while exigent is urgent; needing immediate action.

As a noun exigent is

(archaic) extremity; end; limit; pressing urgency.

As adjectives the difference between sedulous and arduous

is that sedulous is diligent in application or pursuit; constant, steady, and persevering in business or in endeavors to effect an object; steadily industrious; assiduous while arduous is needing or using up much energy; testing powers of endurance.

As adjectives the difference between insurmountable and arduous

is that insurmountable is incapable of being passed over, surmounted, or overcome; insuperable; as, insurmountable difficulty or obstacle while arduous is needing or using up much energy; testing powers of endurance.

As a noun predicament

is a definite class, state or condition.

As an adjective arduous is

needing or using up much energy; testing powers of endurance.

As a noun remark

is act of pointing out or attentively noticing; notice or observation or remark can be a mark that replaces another mark.

As a verb remark

is to make a remark or remarks; to comment or remark can be to mark again (a piece of work).

As an adjective arduous is

needing or using up much energy; testing powers of endurance.

As adjectives the difference between arduous and hardened

is that arduous is needing or using up much energy; testing powers of endurance while hardened is unfeeling or lacking emotion due to experience; callous.

As a verb hardened is

past tense of harden.

As an adjective arduous

is needing or using up much energy; testing powers of endurance.

As a noun cynics is

.