Chimaera (Chimera)

Three mentions:

Earth’s winged chimaeras are Truth’s steeds in Heaven,
The impossible God’s sign of things to be.
     — Book 1 Canto 4

The Chimera is the symbol of unconsciousness and darkness, and consequently of illusions. (See The Hour Before the Gods Awake)

Chimera Chimera

Chimera Apulia. Louvre Museum. Public domain

In common parlance, it is also used to mean a thing impossible to achieve, a daydream.

Chimera is depicted winged, so it is a mental ideation.