in four by four days or every four days (see Molina)
Orthographic Variants:
nanauilhuitica
Alonso de Molina:
nanauilhuitica. de quatro en quatro dias, o cada quatro dias. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 063r. col. 1. Thanks to Joe Campbell for providing the transcription.