(n.) a song or poem celebrating the return of spring
A reverdie is a song or poem, or similar composition, intended to celebrate the return of spring at the end of winter.
That’s a word borrowed into English in the the 1800s, but in its native French reverdies have been written since medieval times, and the word itself has been in recorded use since the thirteenth century. It seems to have fallen out of favour in the Middle Ages, however, before the word—and presumably the written form it describes—were revived in more recent centuries, and presumably imported into English around the same time: the Oxford English Dictionary explains the word “apparently shows a revival” of a much older term in nineteenth century French.
Etymologically, reverdie derives from the same roots as vert, the French for ‘green’: verdir is a French verb meaning ‘to become green’, and so reverdie literally refers to the ‘re-greening’ of the landscape in the spring, after the winter snows and frosts have finally thawed.