something that is harmful to one's health, poisonous, can damage or put an end to morality, long ritual practices (see Molina)
Alonso de Molina:
iztlacyo. cosa ponzoñosa. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 49v. col. 2. Thanks to Joe Campbell for providing the transcription.