sinking feeling vs sinking

sinking feeling and sinking both are nouns.

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

As nouns, sinking feeling and sinking are synonyms defined as:

sinking feeling and sinking: a feeling caused by uneasiness or apprehension

sinking feeling (noun)	sinking (noun)
a feeling caused by uneasiness or apprehension	a descent as through liquid (especially through water)
	a slow fall or decline (as for lack of strength)
	a feeling caused by uneasiness or apprehension