bad words -- from a- (not), cualli (good), and tlahtolli (words) (see Molina)
Orthographic Variants:
aquallatolli, aquallahtolli, acuallahtolli
Alonso de Molina:
aquallatolli. palabras malas. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 7r. col. 1. Thanks to Joe Campbell for providing the transcription.