hiatus vs subsidence

hiatus and subsidence both are nouns.

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

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

hiatus: an interruption in the intensity or amount of something
subsidence: an abatement in intensity or degree (as in the manifestations of a disease)

Other hyponyms of hiatus include defervescence, remission, remittal.

hiatus (noun)	subsidence (noun)
a natural opening or perforation through a bone or a membranous structure	a gradual sinking to a lower level
a missing piece (as a gap in a manuscript)	the sudden collapse of something into a hollow beneath it
an interruption in the intensity or amount of something	an abatement in intensity or degree (as in the manifestations of a disease)