pactum

A pactum de contrahendo requires likewise the mutual consent of the parties.

But such punctationes must not be confounded either with a preliminary treaty or with a so-called pactum de contrahendo.

Otherwise, it would be simply a nudum pactum—a vow without consideration.

His favourite device was Pactum serva, "Keep your promise," and in all his doings he strove to carry it out.