ceaselessness vs endlessness

ceaselessness and endlessness both are nouns.

Word	Noun	Adjective	Verb	Adverb
ceaselessness	Yes	No	No	No
endlessness	Yes	No	No	No

As nouns, endlessness is a hypernym of ceaselessness; that is, endlessness is a word with a broader meaning than ceaselessness:

ceaselessness: the quality of something that continues without end or interruption
endlessness: the property of being (or seeming to be) without end

ceaselessness (noun)	endlessness (noun)
the quality of something that continues without end or interruption	the property of being (or seeming to be) without end