extremity vs hard knocks

extremity and hard knocks both are nouns.

Word	Noun	Adjective	Verb	Adverb
extremity	Yes	No	No	No
hard knocks	Yes	No	No	No

As nouns, hard knocks is a hypernym of extremity; that is, hard knocks is a word with a broader meaning than extremity:

extremity: an extreme condition or state (especially of adversity or disease)
hard knocks: a state of misfortune or affliction

Other hypernyms of extremity include adversity, hardship.

extremity (noun)	hard knocks (noun)
an external body part that projects from the body	a state of misfortune or affliction
that part of a limb that is farthest from the torso
the outermost or farthest region or point
the greatest or utmost degree
an extreme condition or state (especially of adversity or disease)