a hand cloth (see Molina); but the tilmatli addition suggests it could be big, even like a cloak
Orthographic Variants:
nemapopoaloni tilmatli
Alonso de Molina:
nemapopoaloni tilmatli. paño de manos, o touaja. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 67r. col. 1. Thanks to Joe Campbell for providing the transcription.