fixing vs upkeep

fixing and upkeep both are nouns.

Word	Noun	Adjective	Verb	Adverb
fixing	Yes	No	No	No
upkeep	Yes	No	No	No

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

fixing (noun)	upkeep (noun)
the act of putting something in working order again	activity involved in maintaining something in good working order
the sterilization of an animal	the act of sustaining life by food or providing a means of subsistence
(histology) the preservation and hardening of a tissue sample to retain as nearly as possible the same relations they had in the living body
restraint that attaches to something or holds something in place