to make foam or froth, to become foamy (see Molina)
IPAspelling:
posoːnɑltiɑ
Alonso de Molina:
pozonaltia. nitla. (pret. onitlapozonalti.) hazer espuma. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 82v. col. 2. Thanks to Joe Campbell for providing the transcription.