metztlapohua.

In ye huecauh huehuetque catca ynic tlamanitiaya ynic metztlapohuaya ynic quitecpanaya yn inmetz ce xihuitl ynic ontlamia in ye mochi yc quitecpanaya caxtollomey metztli auh çan cenpohualilhuitl quitlaliaya yn ce metztli = In ancient times it was customary for those who were the ancestors to count the months, to arrange their months in order; for a year to be complete they arranged in order eighteen months in all, and they placed only twenty days in a month. (central Mexico, early seventeenth century)
Codex Chimalpahin: Society and Politics in Mexico Tenochtitlan, Tlatelolco, Culhuacan, and Other Nahuatl Altepetl in Central Mexico; The Nahuatl and Spanish Annals and Accounts Collected and Recorded by don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, eds. and transl. Arthur J. O. Anderson and Susan Schroeder (Norman: University of Oklahoma Press, 1997), vol. 2, 126–127.