the first thing, the thing that comes first in line, ahead (see Molina)
Alonso de Molina:
tlayacatia. cosa primera, o delantera. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 120v. col. 2. Thanks to Joe Campbell for providing the transcription.