hiatus vs defervescence

hiatus and defervescence both are nouns.

Word	Noun	Adjective	Verb	Adverb
hiatus	Yes	No	No	No
defervescence	Yes	No	No	No

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

hiatus: an interruption in the intensity or amount of something
defervescence: abatement of a fever as indicated by a reduction in body temperature

Other hyponyms of hiatus include remission, remittal, subsidence.

hiatus (noun)	defervescence (noun)
a natural opening or perforation through a bone or a membranous structure	abatement of a fever as indicated by a reduction in body temperature
a missing piece (as a gap in a manuscript)
an interruption in the intensity or amount of something