ichtaca.

Headword: 
ichtaca.
Principal English Translation: 

secretly

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), 219.

IPAspelling: 
itʃtɑkɑ
Alonso de Molina: 

ichtaca. secretamente, o aescondidas. aduerbio.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 32v. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

ICHTACA secretly / secretamente o a escondidas (M) T has the variant form ICHTECA. With –TZIN there is an intervening glottal stop which does not appear in compounds. The alternation Ā- AH is to be found elsewhere, suggesting that this should be ICHTACĀ, but even in compounds where it is not word-final, the final vowel is never attested long in the sources for this dictionary. See (I)CHTEQU(I).
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 93.

Lockhart’s Nahuatl as Written: 

pret. agentive as adverbial particle. also bound to nouns and verbs. original verb not known. related to ichtequi? 219

Attestations from sources in English: 

ioan qujmanazque qujntzitzqujzque in tetlan nenque in ichtaca oalcalaquj in qujoalnemilia altepetl = And they were to apprehend and seize informers who had entered here in secret, who walked about the city (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 8 -- Kings and Lords, no. 14, Part IX, 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, 1951), 57.

ynic amo moychtacamiquizque = so that they will not secretly kill themselves
Fray Alonso de Molina, Nahua Confraternities in Early Colonial Mexico: The 1552 Nahuatl Ordinances of fray Alonso de Molina, OFM, ed. and trans., Barry D. Sell (Berkeley: Academy of American Franciscan History, 2002), 114–115.

auh no yhquac. yn o iuh qualoc tonatiuh nimãn ic peuh ỹ nican ciudad mexico miyec tlacatl. oychtaca micq̃ in timacehualtin. yhuã españoles. ỹ quimixilia. huel yuh tlamico ỹ xihuitl de 1611. a˚s. yn ichtacamicohuac = And also when the solar eclipse was over, it began that here in the city of Mexico many people were killed by stealth, we commoners and Spaniards who were stabbed. Right until the end of the year of 1611 people were murdered by stealth (central Mexico, 1611)
Annals of His Time: Don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, James Lockhart, Susan Schroeder, and Doris Namala, eds. and transl. (Stanford: Stanford University Press, 2006), 184–5.