inconstant vs variable

inconstant is not a noun while variable is a noun.

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

inconstant (noun)	variable (noun)
	a quantity that can assume any of a set of values
	a symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity
	something that is likely to vary; something that is subject to variation
	a star that varies noticeably in brightness

inconstant (adjective)	variable (adjective)
likely to change frequently often without apparent or cogent reason; variable	liable to or capable of change
	(used of a device) designed so that a property (as e.g. light) can be varied
	marked by diversity or difference