an obstacle or barrier to prevent an invasion or the discovery of something (see Molina and the Diccionario de la Real Academia Española)
IPAspelling:
tɬɑːltenɑntɬi
Alonso de Molina:
tlaltenantli. valladar. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 124v. col. 2. Thanks to Joe Campbell for providing the transcription.