a climbing cord (see Molina); mecatl (cord) is at the root of this construction
Alonso de Molina:
mecatitech tlamatqui. trepador assi. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 55r. col. 1. Thanks to Joe Campbell for providing the transcription.