"Verdant" is a wonderful word. A word first used in print in English in 1581, it means "green." It means green, in the spirit of "sumer is Icumen":
c.1300, "fresh green color," from O.Fr. verdure "greenness," from verd, variant of vert "green," from L. viridis (cf. Sp., It. verde), related to virere "be green," of unknown origin. Perhaps ult. from a root meaning "growing plant" and cognate with Lith. veisti "propagate," O.N. visir "bud, sprout," O.E. wise "sprout, stalk, etc." Meaning "green plants, vegetation" is attested from c.1400.When we learned the song in elementary school, my wonderful music teacher told us that the line bucke uerteþ (pronounced "buck-a verteth") meant that the buck was farting. She suggested that the origins of the word "fart" might have had to do something with eating greens. Etymolgies aside, (perhaps she missed the mark on that one, but the association still remains for me) the idea about the word "fart" being used in a song from the Middle Ages stays implanted in the brain for decades and decades. Perhaps that's one reason it the song has remained in the repertoire.
It is a real hoot to read the online musings about the word "verdant," like this one, and this one. We shouldn't forget that "verdant" (or its more colloquial "green") is nicely represented in song. Some examples are Schubert's setting of Muller's two faces of green in Die liebe farbe and Die bose farbe, Debussy's setting of Verlaine's poem "Green," and the classic reflection on the difficulties associated with actually being green.