zacno.

Headword: 
zacno.
Principal English Translation: 

what's more; this is an adverb that indicates the conversation will continue

Orthographic Variants: 
çacno, zā oc nã
Alonso de Molina: 

zacno. mas tambien aduerbio. para continuar.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 13v. col. 2. Thanks to Joe Campbell for providing the transcription.

Attestations from sources in English: 

zā oc nã = even more so, furthermore [This is traditionally written zacno, with elision of the /o/ of oc.]
James Richard Andrews, Introduction to Classical Nahuatl (2003), vol. 1, 44.