to be or become concave, especially when speaking of a bird's beak Gran Diccionario Náhuatl, citing Wimmer (2004), "v.impers., devenir concave, en parlant du bec," who cites the Florentine Codex, Book 11, f. 22. See: https://gdn.iib.unam.mx/diccionario/tenacalihui/62698. Translation here to English by Stephanie Wood.