changeless vs constant

changeless is not a noun while constant is a noun.

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

As adjectives, changeless and constant are synonyms defined as:

Other synonyms of changeless include invariant, unvarying.

changeless (noun)	constant (noun)
	a quantity that does not vary
	a number representing a quantity assumed to have a fixed value in a specified mathematical context

changeless (adjective)	constant (adjective)
not subject or susceptible to change or variation in form or quality or nature	steadfast in purpose or devotion or affection
unvarying in nature	uninterrupted in time and indefinitely long continuing
remaining the same for indefinitely long times	unvarying in nature