Principal English Translation:
the forearm, from the elbow to the wrist (see Molina and Siméon)
Alonso de Molina:
matzotzopaztli. tabla del brazo, desdel codo hasta la muñeca.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 54r. col. 1. Thanks to Joe Campbell for providing the transcription.
Attestations from sources in English:
matzotzopaztli = forearm
patlachtilaoac = long and thick
quatomaoac = flaring toward top
tzimpitzaoac = tapering toward bottom
patlachtic = wide
oapaltic = broad
ic necaltilo = with it there is fighting
ic nemapatlalo = with it there is resistance
tepaleuia = it helps one
tetzacuilia = it defends one (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 10 -- The People, No. 14, Part 11, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1961), 115.
"matztzopaztli" = a fraction of a matl, translated as "un poco, casi media braza"
(San Hipólito Teocaltitlan, Mexico City, 1593)
James Lockhart collection, notes in the file "Land and Economy." For this example he cites AGN Hospital de Jesús 298, no. 4, ff. 5r, 14v.
Attestations from sources in Spanish:
matzotzopaztli (s.) = antebrazo, parte carnosa del brazo, desde el codo hasta la muñeca
Rémi Siméon, Diccionario de la lengua náhuatl o mexicana (Mexico: Siglo XXI, 1988), 263.