manen.

Headword: 
manen.
Principal English Translation: 

let it not be that, beware lest, etc.

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), 224.

Orthographic Variants: 
in manen
IPAspelling: 
mɑːneːn
Alonso de Molina: 

manen. mirad que no. s. se haga tal cosa, aduertiendo. vel. mirad bien y aduertid.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 52r. col. 2. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

MĀNĒN compound introductory particle for clauses expressing admonition let it not be that … , let it be in vain that … / mirad que no … se haga tal cosa, advertiendo, … mirad bien y advertid (M) This serves as a more emphatic introductory particle than simple MĀ with the admonitive. If the following clause includes explicit negation, in addition to the admonitive construction itsejf, MĀNĒN creates a double negative which serves to affirm rather than to negate. See MĀ, NĒN.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 136.

Lockhart’s Nahuatl as Written: 

mānēn, particle. less ambiguous and more emphatic than mā with the vetitive, mā, nēn in vain. 224