endless vs sempiternal

endless and sempiternal both are adjectives.

Word	Noun	Adjective	Verb	Adverb
endless	No	Yes	No	No
sempiternal	No	Yes	No	No

As adjectives, endless and sempiternal are synonyms defined as:

endless and sempiternal: having no known beginning and presumably no end

Other synonyms of endless include dateless.

endless (adjective)	sempiternal (adjective)
having the ends united so as to form a continuous whole	having no known beginning and presumably no end
having no known beginning and presumably no end
tiresomely long; seemingly without end
infinitely great in number