ultimacy vs extremity

ultimacy and extremity both are nouns.

Word	Noun	Adjective	Verb	Adverb
ultimacy	Yes	No	No	No
extremity	Yes	No	No	No

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

ultimacy: the state or degree of being ultimate; the final or most extreme in degree or size or time or distance
extremity: the greatest or utmost degree

Other hyponyms of ultimacy include profoundness.

ultimacy (noun)	extremity (noun)
the state or degree of being ultimate; the final or most extreme in degree or size or time or distance	an external body part that projects from the body
	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)