strength vs hardiness

strength and hardiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
strength	Yes	No	No	No
hardiness	Yes	No	No	No

As nouns, hardiness is a hyponym of strength; that is, hardiness is a word with a more specific, narrower meaning than strength:

strength (noun)	hardiness (noun)
the property of being physically or mentally strong	the property of being strong and healthy in constitution
an asset of special worth or utility	the trait of being willing to undertake things that involve risk or danger
permanence by virtue of the power to resist stress or force
the amount of energy transmitted (as by acoustic or electromagnetic radiation)
capability in terms of personnel and materiel that affect the capacity to fight a war
physical energy or intensity
capacity to produce strong physiological or chemical effects
the power to induce the taking of a course of action or the embracing of a point of view by means of argument or entreaty
the condition of financial success