subsiding vs subsidence

subsiding and subsidence both are nouns.

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

As nouns, subsiding and subsidence are synonyms defined as:

Other synonyms of subsiding include settling.

subsiding (noun)	subsidence (noun)
a gradual sinking to a lower level	a gradual sinking to a lower level
	the sudden collapse of something into a hollow beneath it
	an abatement in intensity or degree (as in the manifestations of a disease)