the waning moon (literally, already dying) (see Molina)
Orthographic Variants:
ye mictiuh ym metztli
Alonso de Molina:
ye mictiuh ym metztli. menguante de luna. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 35v. col. 1. Thanks to Joe Campbell for providing the transcription.