constant vs invariable

constant and invariable both are nouns.

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

As nouns, constant and invariable are synonyms defined as:

Other synonyms of constant include constant quantity.

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

constant (adjective)	invariable (adjective)
steadfast in purpose or devotion or affection	not liable to or capable of change
uninterrupted in time and indefinitely long continuing
unvarying in nature