auh.

Headword: 
auh.
Principal English Translation: 

and; but; well; or, an indicator of a new thought to follow (not always translated)

Orthographic Variants: 
aho, ahu, hau
Alonso de Molina: 

auh, y. conjunction copulatiua.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 9r. col. 2. Thanks to Joe Campbell for providing the transcription.

Horacio Carochi / English: 

auh = particle indicating the beginning of a new independent statement
Horacio Carochi, S.J., Grammar of the Mexican language with an explanation of its adverbs (1645), translated and edited with commentary by James Lockhart, UCLA Latin American Studies Volume 89 (Stanford: Stanford University Press, UCLA Latin American Center Publications, 2001), 458-59 and n4, 498.

āuh = well, very well
Horacio Carochi, S.J., Grammar of the Mexican language with an explanation of its adverbs (1645), translated and edited with commentary by James Lockhart, UCLA Latin American Studies Volume 89 (Stanford: Stanford University Press, UCLA Latin American Center Publications, 2001), 458–61, 498.

Attestations from sources in English: 

auh. particle. beginning of a new independent statement; indicates that a pause (a period) came just before, although exceptions are found. Generally translated "and," sometimes "but," often not translated except by a period and a capital letter.
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 211.

ahu in axcan Camo ticpie = and now we are no longer have
ahu quemotlania Anparo de poseSion = and he demands affirmation of possession (Azcapotzalco, 1738)
Beyond the Codices, eds. Arthur J.O. Anderson, Frances Berdan, and James Lockhart (Los Angeles: UCLA Latin American Center, 1976), Doc. 17, 102–103.

Also spelled aho.
Thelma Sullivan, Documentos Tlaxcaltecas del siglo XVI en lengua náhuatl (Mexico: Universidad Nacional Autónoma de México, 1987), 30.

hau yntla onpa namacoz = and if he is hired out in Puebla (Tlaxcala, 1547)
Beyond the Codices, eds. Arthur J.O. Anderson, Frances Berdan, and James Lockhart (Los Angeles: UCLA Latin American Center, 1976), Doc. 22, 118–119.

ahu quemotlanja Anparo de poseSion = and he demands affirmation of possession (Azcapoltzaclo, 1738)
Beyond the Codices, eds. Arthur J.O. Anderson, Frances Berdan, and James Lockhart (Los Angeles: UCLA Latin American Center, 1976), Doc. 17, 102–103.

ahu in axcan Cacmo ticpie = and now we no longer have (Azcapotzalco, 1738)
Beyond the Codices, eds. Arthur J.O. Anderson, Frances Berdan, and James Lockhart (Los Angeles: UCLA Latin American Center, 1976), Doc. 17, 102–103.

auh inin = and this -- a phrase in the play Holy Wednesday to "introduce a closing statement to a shorter segment of discourse"
Louise M. Burkhart, Holy Wednesday: A Nahua Drama from Early Colonial Mexico (Philadelphia: University of Pennsylvania Press, 1996), 168.

Attestations from sources in Spanish: 

Yu neci = Auh neci = Como lo muestra (Guatemala, 1637, documento en pipil)
Miguel León-Portilla, "Un Texto en Nahua Pipil de Guatemala, Siglo XVII," Estudios de Cultura Náhuatl 13 (1978), 35–47, y ver 44–45.