to know with certainty, or to have an understanding (see Molina)
Alonso de Molina:
mayuh ye in amoyollo. sey ciertos o tened entendido. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 51v. col. 1. Thanks to Joe Campbell for providing the transcription.