tequixquitl.

Headword: 
tequixquitl.
Principal English Translation: 

translated variously as: potassium nitrate, sodium chloride and carbonate, or saltpeter; used in medicinal treatments

IPAspelling: 
tekiːʃkitɬ
Alonso de Molina: 

tequixquitl. salitre.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 105v. col. 2. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

TEQUĪXQUI-TL a naturally occurring efflorescent carbonate of soda used in laundry, preparation of food, and medicinally / tequesquite, polvo para limpiar (Z) [(1)Tp.226, (2)Zp.121,222]. T has a short vowel in the second syllable. This is probably related to the fact that T idiosyncratically has a short vowel in QUĪXTIĀ< QUĪZ(A) 'to come out.' M has tequizqui 'something petrified, solidified.' See TE-TL, QUĪZ(A).
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 233.

Attestations from sources in Spanish: 

yhuan yn ixqui in petlatolli yhuan in çacatl yhuan in tequixquitl = y todo es tierra de junco o tule, enzacatada y salitrosa (Culhuacan, 1580)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 2, Testamentos en náhuatl y castellano del siglo XVI, eds., Teresa Rojas Rabiela, Elsa Leticia Rea López, Constantino Medina Lima (Mexico: Consejo Nacional de Ciencias Tecnología, 1999), 226–227.

petlatolli zacatl tequixquitl = petlatolli, zacatl, tequixquitl (tule, zacate, tequesquite) (Culhuacan, 1580)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 2, Testamentos en náhuatl y castellano del siglo XVI, eds., Teresa Rojas Rabiela, Elsa Leticia Rea López, Constantino Medina Lima (Mexico: Consejo Nacional de Ciencias Tecnología, 1999), 222–223.