Definitions

1. adjective

Having or showing a tendency to become covered with feathers, especially in relation to birds.

“The impennous plumage of the young bird was a sign of its imminent growth into a fully-fledged adult.”

2. noun

A young bird that is in the process of growing feathers, especially one that is not yet fully grown.

“The impennous fledglings were chirping excitedly in the nest.”