Food of Love: This song is actually originally a monologue which comes from Act I Scene 1 of Twelfth Night. In the opening scene, Orsino, the Duke of Illyria, is in love. The play opens with him listening to a musical ensemble. At the top of the scene, it seems the players have stopped and he tells them to play until he gets sick of it. He reasons that if music is the food of love, if he overstuffs himself with it, as with food, he may get sick and lose his appetite for love for Olivia. But he continues to indulge in his feelings of love, setting the scene for this love-centered play. 

thrice crowned Queene of night: The moon goddess ruled as Cynthia in the heavens, Diana on earth, and Proserpina in the underworld. *crownèd

Thy Huntress' name: Orlando imagines Rosalind as one of the followers of Diana (who was also the goddess of chastity).

sway: control

character: inscribe

unexpressive: inexpressible, indescribable