achtli.

Headword: 
achtli.
Principal English Translation: 

elder brother (from the point of view of a younger sister) (see Karttunen)

Orthographic Variants: 
āchtli
IPAspelling: 
ɑːtʃtɬi
Frances Karttunen: 

ĀCH-TLI elder brother (from the point of view of a younger sister) / hermano mayor de la hermana menor (C) [(1)Cf.126v,(1)Rp.59]. This seems to be related ACHTO ´first,´but there is a vowel-length discrepancy. It contrasts in vowel length with ACH-TLI ´seed´.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 3.

Lockhart’s Nahuatl as Written: 

nachtzin = the older brother of a woman specifically
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), 48.