the sole of a shoe, or the middle section that covers the arch of the feet (see Molina)
Alonso de Molina:
xocpalquimiliuhcayotl. peal o escarpin. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 160v. col. 2. Thanks to Joe Campbell for providing the transcription.