deficient vs deficiency

deficient is not a noun while deficiency is a noun.

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

deficient (noun)	deficiency (noun)
	lack of an adequate quantity or number
	the state of needing something that is absent or unavailable

deficient (adjective)	deficiency (adjective)
of a quantity not able to fulfill a need or requirement
inadequate in amount or degree
falling short of some prescribed norm