to go to the other side of the river or sea (see Molina, who gives the example in the first person singular)
Orthographic Variants:
ateputzco niauh, atepotzco niauh
Alonso de Molina:
ateputzco niauh (pret. ateputzco onia.) yr dela otra parte del rio o mar. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 7v. col. 2. Thanks to Joe Campbell for providing the transcription.