the film or skin on boiled milk, the top layer or a foam like substance on milk (see Molina)
Alonso de Molina:
iyolcayo. lama o nata. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 36v. col. 2. Thanks to Joe Campbell for providing the transcription.