A more thorough explanation:

Definition: To name or pronounce something out loud.

Example: When a person writes a will, they may nuncupare their chosen heir by announcing their name in front of witnesses.

This means that when someone wants to officially name or declare something, they can do so by saying it out loud in front of others. This was often done in legal settings, such as when creating a will, to ensure that the declaration was witnessed and recorded accurately.