Indorsament or indorsument?

Unable to post yesterday because in the evening was midterms for Negotiable Instruments Law, and Credit Transactions. And before that we had a simple lunch out with the family and two guests to celebrate our 28th wedding anniversary. From that my age as a law student may be estimated.

For today we have from page 112 of De Leon and De Leon's The Law on Negotiable Instruments (With Documents of Title) 2013 Edition: 

I think that the De Leons got their idea from this passage on page 110 of the Law of Negotiable Instruments, Second Edition, 1922  by James Ogden:

Ogden, however, used two words while De Leon coupled the words into one. Both are not exactly accurate as to the English translation. Dorsa is plural for dorsum. So in dorsa, or indorsa per De Leon, would mean on the backs. In dorsum, on the other hand, would be just a few steps away from indorsement.

Ogden's book is available for download here.