a nose ornament (see attestations)
y yacametz = his nose ornament in the form of a crescent. (central Mexico, sixteenth century)
"...vessels made for drinking pulque during ceremonies often have rabbit symbolism and/or a crescent, half-moon shape symbol called the yacametztli."
auh in inechichihual tezcatzoncatl, aztatzone, yacametze, amanacoche = "and the array of tezcatzoncatl [was thus]: he had the white heron feather headdress; he had the crescent-shaped nose ornament, the ear plug of paper. (Florentine Codex, b.1 f.3 p.51)