yacatto.

Headword: 
yacatto.
Principal English Translation: 

first, or firstly (an adverb) (see Molina)

IPAspelling: 
jɑkɑtto
Alonso de Molina: 

yacatto. primero o primeramente. aduerbio.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 30v. col. 1. Thanks to Joe Campbell for providing the transcription.

Attestations from sources in English: 

Ye quitohuaya in dios quiyocoya yeehuaya yacatto yehuatl in tlanexxtli ya ynic omilhuitl ye quichiuh in ilhuicatlo ohuiya. = God says it, and he creates it: first was the light. And on the second day he made the sky.
John Bierhorst, Cantares Mexicanos: Songs of the Aztecs (Stanford: Stanford University Press, 1985), 268–269.