indorsement vs promo

indorsement and promo both are nouns.

Word	Noun	Adjective	Verb	Adverb
indorsement	Yes	No	No	No
promo	Yes	No	No	No

As nouns, promo is a hypernym of indorsement; that is, promo is a word with a broader meaning than indorsement:

indorsement: a promotional statement (as found on the dust jackets of books)
promo: a message issued in behalf of some product or cause or idea or person or institution

Other hypernyms of indorsement include packaging, promotion, promotional material, publicity.

indorsement (noun)	promo (noun)
the act of endorsing	a message issued in behalf of some product or cause or idea or person or institution
formal and explicit approval
a promotional statement (as found on the dust jackets of books)
a speech seconding a motion
a signature that validates something