nempanca.

Headword: 
nempanca.
Principal English Translation: 

something without a clear outcome or benefit, something in vain (see Karttunen)

Orthographic Variants: 
nēmpancah
IPAspelling: 
neːmpɑnkɑh
Alonso de Molina: 

nempanca. cosa sin prouecho, o por demas.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 67v. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

NĒMPANCAH something without a clear outcome or benefit, something in vain / cosa sin provecho o por demás (M) usarse cuando uno pretende hacer algo y dudando si le ha de salir bien, se resuelve a cometerle (C) [(5)Cf.122r,123r,131v]. See NĒN, -PAN, the verb CĀ.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 166.

Horacio Carochi / English: 

nēmpancâ = particle, implying going ahead and doing something regardless of the results
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), 507.