invariable vs changeless

invariable is a noun but changeless is not a noun.

Word	Noun	Adjective	Verb	Adverb
invariable	Yes	Yes	No	No
changeless	No	Yes	No	No

invariable (noun)	changeless (noun)
a quantity that does not vary

invariable (adjective)	changeless (adjective)
not liable to or capable of change	not subject or susceptible to change or variation in form or quality or nature
	unvarying in nature
	remaining the same for indefinitely long times