Emily Dickinson Lexicon

PA-PIL-I-O-NA'CEOUS, a.

Resembling the butterfly; a term in botany, used to describe the corols of plants which have the shape of a butterfly, such as that of the pea. The papilionaceous plants are of the leguminous kind. Encyc. Quiny. The papilionaceous corol is usually four-petaled, having an upper spreading petal, called the banner, two side petals, called wings, and a lower petal called the keel. – Martyn.