survival of the fittest vs natural selection

survival of the fittest and natural selection both are nouns.

Word	Noun	Adjective	Verb	Adverb
survival of the fittest	Yes	No	No	No
natural selection	Yes	No	No	No

As nouns, survival of the fittest and natural selection are synonyms defined as:

survival of the fittest and natural selection: a natural process resulting in the evolution of organisms best adapted to the environment

Other synonyms of survival of the fittest include selection, survival.

survival of the fittest (noun)	natural selection (noun)
a natural process resulting in the evolution of organisms best adapted to the environment	a natural process resulting in the evolution of organisms best adapted to the environment