a feather-covered ornament; or, a tree-like structure with lots of rare feathers and quetzal feathers; also, perhaps a quetzal-feather head fan
See an image that represents petlacotl in the Visual Lexicon of Aztec Hieroglyphs, ed. Stephanie Wood (Eugene, Ore.: Wired Humanities, 2020-present).
This same term is used in the Codex Sierra-Texupan in combination with "manga" (Spanish for "sleeve") to describe a woven black covering for a Christian cross that would be carried to burials. No mention is made of feathers. Perhaps the clergy would not allow the cross to be decorated with feathers in this situation.
John Bierhorst draws hypothetical relationships between petlacotl, petlacomitl, and petlacontli--terms that do not appear in Molina's dictionary.