approval vs endorsement

approval and endorsement both are nouns.

Word	Noun	Adjective	Verb	Adverb
approval	Yes	No	No	No
endorsement	Yes	No	No	No

As nouns, endorsement is a hyponym of approval; that is, endorsement is a word with a more specific, narrower meaning than approval:

approval (noun)	endorsement (noun)
the formal act of approving	the act of endorsing
a message expressing a favorable opinion	formal and explicit approval
a feeling of liking something or someone good	a promotional statement (as found on the dust jackets of books)
acceptance as satisfactory	a speech seconding a motion
	a signature that validates something