it is one being comprised of the three divine persons; or, it is one essence (referring to the Catholic view of the Holy Trinity) (see Molina)
Alonso de Molina:
cettitica. es vno el ser delas tres personas diuinas, o es vna su essencia. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 18v. col. 1. Thanks to Joe Campbell for providing the transcription.