indorsement vs imprimatur

indorsement and imprimatur both are nouns.

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

As nouns, indorsement and imprimatur are synonyms defined as:

Other synonyms of indorsement include countenance, endorsement, sanction, warrant.

indorsement (noun)	imprimatur (noun)
the act of endorsing	formal and explicit approval
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