-hua.

Headword: 
-hua.
Principal English Translation: 

(an ending for the impersonal form of an intransitive verb with an indefinite subject; usually adds length to the final vowel of the stem)

Michel Launey, An Introduction to Classical Nahuatl, translated and adapted by Christopher MacKay (Cambridge: Cambridge University Press, 2011), 139.

Attestations from sources in English: 

Cochīhua = Someone's sleeping, everyone's sleeping
Tlācatīhuac = There were births
Temōhuaz = People will descend
pācohua = there's rejoicing (pāqui)
Michel Launey, An Introduction to Classical Nahuatl, translated and adapted by Christopher MacKay (Cambridge: Cambridge University Press, 2011), 139–140.

Cochīhua = Someone's sleeping, everyone's sleeping, Otzàtzihuac = Someone shouted, there was shouting, Tlācatihuac = There were births, Temōhuaz = People will descend
Michel Launey, An Introduction to Classical Nahuatl, translated and adapted by Christopher MacKay (Cambridge: Cambridge University Press, 2011), 139.

This ending can have verb tenses added to it, e.g. -huac, -huaz, etc.
If the last consonant of the stem is "c" (i.e. verbs ending in -ca or -qui), then the vowel before the -hua will be "o."
Michel Launey, An Introduction to Classical Nahuatl, translated and adapted by Christopher MacKay (Cambridge: Cambridge University Press, 2011), 139.