petlacalmecahuehuetl.

Headword: 
petlacalmecahuehuetl.
Principal English Translation: 

a spinet, an old-fashioned stringed musical instrument with keys

Orthographic Variants: 
petlacal mecaueuetl, petlacal mecauehuetl
Alonso de Molina: 

petlacal mecaueuetl. monacordio.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 81r. col. 1. Thanks to Joe Campbell for providing the transcription.