ma.

Headword: 
ma.
Principal English Translation: 

let, may, whether it be, is (optative); can be used in a negative sentence (let not...)

IPAspelling: 
mɑː
Alonso de Molina: 

ma. es particula de optatiuo. s. o si. y de imperatiuo, y del auisatiuo, vetatiuo. y entoncesquiere dezir no. maticchiuh, mira que no lo hagas. &c.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 49v. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

MĀ introductory parcicle for clauses expresing wishes, commands, admonitions; negative form: MĀCA ~ MĀCAMŌ let it be that …, may … / es partícula de optativo… y de imperativo y del avisativo, vetativo, y entonces quiere decir no (M) Preceding a verb in the operative or vetative form, this particle implies that a wist is being expressed rather than a direct comand. The negative sense mentioned in M’s gloss in not inherent in MĀ but en the vetative form of the verb, which warns against doing something (Or M may be combining the senses of MĀ and MAH in a single entry.) MĀNĒN is more emphatic with the vetative. With negative wish clauses, MĀCA ~ MĀCAMŌ occurs in place of the sequence *MĀ AHMŌ. TLĀ may occur in place of MĀ whit the optative and TLĀCA ~ TLĀCAMŌ in corresponding negative wish sentences.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 126.

Horacio Carochi / English: 

mā = optative particle
mà = particle indicating the hypothetical
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), 505.

Lockhart’s Nahuatl as Written: 

mā. particle, sign of the optative, may/let. 223
mah. particle to indicate something hypothetical. iuhquin mah, as if it were. ahtleh mah itlah, nothing whatever. 223
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), 223.

Attestations from sources in English: 

Mā ticcuācān in etl = Let's eat the beans;
Mā niquitta in = May I see this, Let me see this;
Mā ontlami in tlaōlli = Let the corn be done with, Never mind if the corn runs out (lit., finishes)
Michel Launey, An Introduction to Classical Nahuatl, translated and adapted by Christopher MacKay (Cambridge: Cambridge University Press, 2011), 80.

aocmo nesia ma pã ma tortillas yn tianquisco ma tienda = no more did either wheat bread or tortillas appear
Here in This Year: Seventeenth-Century Nahuatl Annals of the Tlaxcala-Puebla Valley, ed. and transl. Camilla Townsend, with an essay by James Lockhart (Stanford: Stanford University Press, 2010), 122–123.

se probision rreal ynic aocmo calaquisque cabildo ma quixtiano ma mestiso ma molato ma tliltic ma chino sa mixcahuisque yn masehualtzitzintin = a royal decree that no Spaniard, mestizo, mulatto, black nor chino should enter the cabildo any more. The indigenous exclusively should do it.
Here in This Year: Seventeenth-Century Nahuatl Annals of the Tlaxcala-Puebla Valley, ed. and transl. Camilla Townsend, with an essay by James Lockhart (Stanford: Stanford University Press, 2010), 130–131.

The optative, ma, is a polite way of phrasing the imperative.
Also: ma ... ma = whether, or
Robert Haskett and Stephanie Wood's notes from Nahuatl sessions with James Lockhart and subsequent research.

Attestations from sources in Spanish: 

Yhuan ma cuel ticmocuitlahui, ma tiquelehui yn cuyetl, in huipilli = Y no anheles, no desees la falda, la camisa (la mujer)
Huehuehtlahtolli. Testimonios de la antigua palabra, ed. Librado Silva Galeana y un estudio introductorio por Miguel León-Portilla (México: Secretaría de Educación Pública, Fondo de Cultura Económica, 1991), 68–69.

Yhuan ma muchipa tictemo, ma muchipa tiquelehui, ticnec in qualli nexintli; ma muchipa timopepetla, timotezcahui, ma muchipa timoyecquetz, timoyecchuichiuh = Y no siempre busques, no siempre desees, quieras la buena apariencia, no te estés siempre peinando, no te estés viendo en el espejo; no siempre te arregles, te engalanes
Auh ahmo teca timocayahuaz, ahmo titechichichaz, ahmo titeaaxixaz, ahmo teycpac timomapopohuaz = Y no te mofarás de la gente, no escupirás a las personas, no las orinarás
Huehuehtlahtolli. Testimonios de la antigua palabra, ed. Librado Silva Galeana y un estudio introductorio por Miguel León-Portilla (México: Secretaría de Educación Pública, Fondo de Cultura Económica, 1991), 64–65.