arduous

Unfeeling is a related term of arduous.

As adjectives the difference between unfeeling and arduous

is that unfeeling is without emotion or sympathy while arduous is needing or using up much energy; testing powers of endurance.

Arduous is a related term of obdurate.

In obsolete|lang=en terms the difference between arduous and obdurate

is that arduous is (obsolete) burning; ardent while obdurate is (obsolete) physically hardened, toughened.

As adjectives the difference between arduous and obdurate

is that arduous is needing or using up much energy; testing powers of endurance while obdurate is stubbornly persistent, generally in wrongdoing; refusing to reform or repent.

Stern is a related term of arduous.

As a noun stern

is a star; a small luminous dot that can be seen on the night sky.

As an adjective arduous is

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

As adjectives the difference between arduous and industrious

is that arduous is needing or using up much energy; testing powers of endurance while industrious is hard-working and persistent; worksome.

Arduous is a related term of knotty.

As adjectives the difference between arduous and knotty

is that arduous is needing or using up much energy; testing powers of endurance while knotty is full of knots.

As adjectives the difference between arduous and uphill

is that arduous is needing or using up much energy; testing powers of endurance while uphill is located up a slope or on a hill.

As an adverb uphill is

up a slope, towards higher ground.

As a noun uphill is

an uphill route.

As adjectives the difference between arduous and monotonous

is that arduous is needing or using up much energy; testing powers of endurance while monotonous is having an unvarying tone or pitch.

In obsolete|lang=en terms the difference between arduous and ponderous

is that arduous is (obsolete) burning; ardent while ponderous is (obsolete) dense.

As adjectives the difference between arduous and ponderous

is that arduous is needing or using up much energy; testing powers of endurance while ponderous is heavy, massive, weighty.

As adjectives the difference between complicated and arduous

is that complicated is difficult or convoluted while arduous is needing or using up much energy; testing powers of endurance.

As a verb complicated

is (complicate).

As adjectives the difference between arduous and cardio

is that arduous is needing or using up much energy; testing powers of endurance while cardio is cardiovascular; pertaining to the health of the circulatory and respiratory systems.

As a noun cardio is

cardiovascular exercise.