mach.

Headword: 
mach.
Principal English Translation: 

certainly; justly; totally; a lot; (in a question) by chance? perhaps?; it is said; it appears that (see Molina, Karttunen)

IPAspelling: 
mɑtʃ
Alonso de Molina: 

mach. dizque, o dizen que.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 50v. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

MACH it is said that, it appears that … / dizque o dicen que (M), parece que (C) Bound to an interrogative particle, this serves as an intensifier. C gives its equivalent in Spanish as diablos, hence TLEINMACH ‘what the devil?’ In a question this implies perplexity; in confirming something, it leaves room for doubt.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 127.

Andrés de Olmos: 

Otras vezes esta en lugar de ca, que denota afirmacion en la platica. Ex. : mach amo oniquito, vel ca amo oniquito, cierto no lo dixe. Los de Tlaxcala dizen machmo en lugar de amo.
Andrés de Olmos, Arte para aprender la lengua Mexicana, ed. Rémi Siméon, facsimile edition ed. Miguel León-Portilla (Guadalajara: Edmundo Aviña Levy, 1972), 184.

Attestations from sources in English: 

Canin mach coyonacazco. iquac mitoa: in aca tenaualaoa, tetlacaquitia, in amo cenca quinextia tlatolli. = Where, perhaps, in a coyote's ear? This is said when someone derides and openly criticizes another, but what he says does not reveal much.
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 126–127.

can mach mjto, ac mach qujto, ac mach qujtocaioti, in mjxitl, in tlapatl in octli = How can it be said? Who can it have been who said it? Who can it have been who referred to pulque as jimson weed? (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 6 -- Rhetoric and Moral Philosophy, No. 14, Part 7, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1961), 69.

quen mach huel = How fortunate! (central Mexico, sixteenth century)
Personal communication, James Lockhart, in sessions analyzing Huehuetlatolli.

Attestations from sources in Spanish: 

Este dize Tlaxcala en lugar de cuix? por ventura? interrogatiue, y antenponiendole una o lo tiene el mexicano en lugar de cenca, muy, o muy mucho. Ayuntase a diuersos verbos en tres solos tiempos de indicatiuo que son : imperfecto, perfecto, plusquamperfecto. Ex. : omachnitlaquaya, coma yo mucho.

Otras vezes esta en lugar de quilhmach, que quiere dezir : dizque. Ex. : quilhmach niaz mochan? dizque yre a tu casa?

conjugación, acaso, macha acaso no (ibid).
Thelma Sullivan, Documentos Tlaxcaltecas del siglo XVI en lengua náhuatl (Mexico: Universidad Nacional Autónoma de México, 1987), 40.