to cover something with charcoal (perhaps?) (see Molina)
IPAspelling:
tekonɑlwiɑ
Alonso de Molina:
teconalhuia. nitla. (pret. onitlateconalhui.) encarbonar algo. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 93r. col. 1. Thanks to Joe Campbell for providing the transcription.