it is the reverse; it is the opposite; or, on the contrary (see Molina)
Orthographic Variants:
zan amoyuhqui, çan amo yuhqui, çan amoyuhqui, çan amo iuhqui
Alonso de Molina:
zan amoyuhqui. es al reues, o al contrario. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 14r. col. 1. Thanks to Joe Campbell for providing the transcription.