inconstant vs constancy

inconstant is not a noun while constancy is a noun.

Word	Noun	Adjective	Verb	Adverb
inconstant	No	Yes	No	No
constancy	Yes	No	No	No

inconstant (noun)	constancy (noun)
	the quality of being enduring and free from change or variation
	faithfulness and dependability in personal attachments (especially sexual fidelity)
	(psychology) the tendency for perceived objects to give rise to very similar perceptual experiences in spite of wide variations in the conditions of observation

inconstant (adjective)	constancy (adjective)
likely to change frequently often without apparent or cogent reason; variable