Latin. A codicillary clause. Under the Roman law, wills or testaments, to .be valid, required certain solemnities, which were not necessary to the validity of codicils, and it was, therefore, not unusual for the testator to add to his testament an express clause to the effect that, if his testament should be held invalid as a testament, it should take effect as a codicil. This is what commentators call the codicillary clause. The chief difference between a testament and codicil was this, that in the latter, an heir properly so called could not be nominated. For a historical narrative of the introduction of codicils.