for the moon to be full (round) already (see Molina)
Orthographic Variants:
yeyaualtic metztli
Alonso de Molina:
yeyaualtic metztli. estar ya la luna llena. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 35r. col. 1. Thanks to Joe Campbell for providing the transcription.