The Collaborative International Dictionary of English v.0.48:

Indorsement \In*dorse"ment\, n. [From Indorse; cf.
   Endorsement.] [Written also endorsement.]
   [1913 Webster]
   1. The act of writing on the back of a note, bill, or other
      written instrument.
      [1913 Webster]

   2. That which is written on the back of a note, bill, or
      other paper, as a name, an order for, or a receipt of,
      payment, or the return of an officer, etc.; a writing,
      usually upon the back, but sometimes on the face, of a
      negotiable instrument, by which the property therein is
      assigned and transferred. --Story. Byles. Burrill.
      [1913 Webster]

   3. Sanction, support, or approval; as, the indorsement of a
      rumor, an opinion, a course, conduct.
      [1913 Webster]

   Blank indorsement. See under Blank. Indorser

The Collaborative International Dictionary of English v.0.48:

Endorsement \En*dorse"ment\, n. [Cf. F. endossement.]
   Same as Indorsement.
   [1913 Webster]

WordNet (r) 3.0 (2006):

endorsement
    n 1: a promotional statement (as found on the dust jackets of
         books); "the author got all his friends to write blurbs for
         his book" [syn: endorsement, indorsement, blurb]
    2: a speech seconding a motion; "do I hear a second?" [syn:
       second, secondment, endorsement, indorsement]
    3: formal and explicit approval; "a Democrat usually gets the
       union's endorsement" [syn: sanction, countenance,
       endorsement, indorsement, warrant, imprimatur]
    4: a signature that validates something; "the cashier would not
       cash the check without an endorsement" [syn: endorsement,
       indorsement]
    5: the act of endorsing; "a star athlete can make a lot of money
       from endorsements" [syn: endorsement, indorsement]