endlessly vs unendingly

endlessly and unendingly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
endlessly	No	No	No	Yes
unendingly	No	No	No	Yes

As adverbs, endlessly and unendingly are synonyms defined as:

Other synonyms of endlessly include ceaselessly, continuously, incessantly, unceasingly.

endlessly (adverb)	unendingly (adverb)
continuing forever without end	with unflagging resolve
with unflagging resolve
all the time; seemingly without stopping
(spatial sense) seeming to have no bounds