"melt..."See in text(A Valediction: Forbidding Mourning)
By melt Donne means to disintegrate or liquefy. This metaphor is another reference to Carpe Diem poetry as the speaker here suggests that the two lovers become one. However, “melt” at this time also meant to disperse into particles, to vanish or disappear. Thus, the line proposes that the lovers simultaneously become one and move away from each other. This dual meaning foreshadows the conclusion Donne will draw at the end of the poem.
