to be in eclipse (a verb, referring to the moon) (see Molina); literally, the moon is eaten; see also qualometztli
Orthographic Variants:
metztli qualo
Alonso de Molina:
metztli qualo. eclipsarse la luna. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 55v. col. 2. Thanks to Joe Campbell for providing the transcription.