greene wood: wood or forest in leaf

turne: tune

his merrie Note / unto the sweet Birds throte: imitate the warbling of the birds. The repetition of "Come hither" may be a verbalization of a particular bird's song.

melancholly: Music was often associated with romantic melancholy.

Weazel suckes egges: The weasel, an animal noted for ferocity, sometimes steals eggs from birds' nests.

i'the Sunne: free from care or sorrow

&c.: An instruction to repeat the lyrics of the last two lines "Come hither..." to the end of the song.

in despight of my Invention: without using my imagination

Ducdame: This is answered by Jaques in his response to the question "What's that Ducdame?", he responds that it is "Greek" meaning "gibberish".

all the first borne of Egypt: "They were all slain by the Angel of Death when Pharaoh refused to free the Israelites" (Exodus 11:5)