From page 1 of the Civil Code of the Philippines Annotated, Vol. V, 2013 Edition:
Google Translate says that sale in Latin is venditionem or venditio. Not avenditionem nor avenditio.
Duhaime's Legal Dictionary translates venditio as a sale. Notice the space between the article and the noun.
Here's how Duhaime defines venditio:
A term of ancient Roman law but still reflected in the civil law and French language for which the verb for sale is vendre and the noun vente. Even in English, a seller is known alternatively as a vendor. In Latin, a male seller is a venditor and a female, venditrix.So how did Paras come up with avenditio? This passage from the book A Text-Book of Roman Law: From Augustus to Justinian By W. W. Buckland may explain:
The old editions of Paras contain the same word. I'd like to believe that this is just proofreading oversight. But who knows?