nemontemi.

The days were seen as having no purpose, no usefulness, and were unlucky. They were the extra five days in the solar year, rounding out the calendar of 18 times 20 (360). No one was supposed to get involved in activities (such trade, marriage, or even sex) during this "week." Debate surrounds whether these five days occurred at the beginning or the end of the year or if they were sprinkled throughout the year.
Juan José Batalla, Mexicolore question about the Aztec calendar answered and published in March 2007. http://www.mexicolore.co.uk/aztecs/ask-experts/when-did-the-5-useless-da...

yhuan ipan oc macuililhuitl quitocayotiaya in huehuetque nemontemi çan tetzallan actica acampa Tetech pouhqui ynic mihtohua çan netemi in macuililhuitl = And there were five more days that the ancestors named "nemontemi" just inserted among them. Nowhere did they correspond to anyone. Hence the five days were said to be filled to no purpose. (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, 119–121; see also 126–127.

The last five days in the count of the 365–day calendar were "generally considered inauspicious."
Lori Boornazian Diel, The Codex Mexicanus: A Guide to Life in Late-Sixteenth-Century New Spain (Austin: University of Texas Press, 2018), 173.

"Los días nemontemi refieren a los días de entidades vinculadas simbólicamente a lo femenino (y diosas particulares) y a seres animados por una fuerza distinta a la solar. Al suspenderse el régimen del sol (simbólicamente por el fin del calendario o por un eclipse), estas entidades femeninas se activan (por pertenecer a la 'obscuridad', lo no-diurno, lo no-solar). A la región donde se oculta el sol (nuestro 'poniente') en náhuatl se le solía llamar 'Cihuatlampa' ('Rumbo de las mujeres'). Al desactivarse la animación del sol (tonalli) se activa la animación 'femenina'. Los nemontemi se refiere as un periodo regido por una animación distinta; creo que esto ha escapado a la perspectiva no sólo de Sahagún y otras fuentes coloniales sino también a los propios estudiosos hasta hoy. Al definirse 'nen' adverbialmente como 'en vano' o 'inútilmente' es muy probable que estemos ante una definición patriarcal de 'femeninamente'. Son días femeninos, días-mujer, días de fuerzas femeninas, días-diosas."
Heriberto Martínez Yépez, "Sueñan los marxistas con revoluciones aztecas? Poéticas del náhuatl y el México de Karl Marx y Walter Benjamin," Ph.D. Dissertation, University of California, Berkeley, 2018, 140.