deficiency vs dearth

deficiency and dearth both are nouns.

Word	Noun	Adjective	Verb	Adverb
deficiency	Yes	No	No	No
dearth	Yes	No	No	No

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

Other hyponyms of deficiency include absence, famine, shortage, deficit, mineral deficiency, shortness, stringency, tightness.

deficiency (noun)	dearth (noun)
lack of an adequate quantity or number	an insufficient quantity or number
the state of needing something that is absent or unavailable	an acute insufficiency