to get dark, to become night (see Molina); also, to be in darkness (see Sahagún, attestations)
Orthographic Variants:
tlaioaticac
Alonso de Molina:
tlayoaticac. (pret. otlayoaticaca.) hazer escuro. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 122r. col. 1. Thanks to Joe Campbell for providing the transcription.