yacachto.

Headword: 
yacachto.
Principal English Translation: 

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

Alonso de Molina: 

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

Attestations from sources in English: 

A range of terms are attested to mean first, such as acatto, accato, achto, acachto, acachtopa, achtotipa, yacachto, yacatto, and yacattopa. The root yacatl (nose) plays a role in some of these words, in the sense that the nose precedes us, it leads, it goes first.

Yehuantin yacachto tequitizque. = Ellos primero pagarán el tributo.
Patrick Johansson K., La palabra, la imagen, y el manuscrito (Mexico: Universidad Nacional Autónoma de México, 2004), 359.

themes: 
Anatomy
Numbers, Math