a vain thing, or something superfluous (see Molina)
Orthographic Variants:
çannenca
Alonso de Molina:
zannenca. cosa vana, o superflua. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 14v. col. 1. Thanks to Joe Campbell for providing the transcription.