a foreign thing, an alien thing; or, something that belongs to someone else (see Molina)
Alonso de Molina:
tecococauh. cosa agena o de otro. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 93r. col. 1. Thanks to Joe Campbell for providing the transcription.