drop in the ocean vs deficiency

drop in the ocean and deficiency both are nouns.

Word	Noun	Adjective	Verb	Adverb
drop in the ocean	Yes	No	No	No
deficiency	Yes	No	No	No

As nouns, deficiency is a hypernym of drop in the ocean; that is, deficiency is a word with a broader meaning than drop in the ocean:

drop in the ocean: an effort or action having very little overall influence, especially as compared to a huge problem.
deficiency: lack of an adequate quantity or number

Other hypernyms of drop in the ocean include inadequacy, insufficiency.

drop in the ocean (noun)	deficiency (noun)
an effort or action having very little overall influence, especially as compared to a huge problem.	lack of an adequate quantity or number
	the state of needing something that is absent or unavailable