sinking vs decrease

sinking and decrease both are nouns.

Word	Noun	Adjective	Verb	Adverb
sinking	Yes	No	No	No
decrease	Yes	No	Yes	No

As nouns, decrease is a hypernym of sinking; that is, decrease is a word with a broader meaning than sinking:

Other hypernyms of sinking include drop-off, lessening.

sinking (noun)	decrease (noun)
a descent as through liquid (especially through water)	the act of decreasing or reducing something
a slow fall or decline (as for lack of strength)	the amount by which something decreases
a feeling caused by uneasiness or apprehension	a change downward
	a process of becoming smaller or shorter

sinking (verb)	decrease (verb)
	decrease in size, extent, or range
	make become smaller