natural spring vs outflow

natural spring and outflow both are nouns.

Word	Noun	Adjective	Verb	Adverb
natural spring	Yes	No	No	No
outflow	Yes	No	No	No

As nouns, natural spring and outflow are synonyms defined as:

Other synonyms of natural spring include fountain, outpouring, spring.

natural spring (noun)	outflow (noun)
a natural flow of ground water	the discharge of a fluid from some container
	a natural flow of ground water
	the process of flowing out