for something to get fat, thick; or, for something to grow (see Molina)
Orthographic Variants:
motomaua
Alonso de Molina:
motomaua. (pret. omotomauh) engordar, o crecer alguna cosa. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 060v. col. 2. Thanks to Joe Campbell for providing the transcription.