Bitter (adjective)
sharp, unpleasant (used to describe taste); figuratively, to describe an emotion that causes hurt or resentment.
In this context, the "sweetness" of the dream is tinged with bitterness, because the promise the dream holds out is not accessible in reality.
Paradise (noun)
Originally meaning walled garden, the concept of paradise has roots in the Judeo-Christian concept of “Heaven,” an afterlife experience of eternal joy, given by God as a reward to his faithful followers.
In the poem, Rossetti employs “Paradise” to stir up other-worldly, even divine connotations. She also means to reference John Milton’s famous epic poem, Paradise Lost.
Brimful (adjective)
full to capacity
Ex. “The theater was brimful of people eager to watch the movie.”
Rounded
Both having a smooth curved surface, and being well-developed and balanced in all aspects.
Echo
Several definitions are important for Rossetti’s titular word
Noun
a. a series of repetitions of sound caused by the reflection of sound waves off of surfaces
b. the repetition of an idea, feeling, concept, etc.
Verb
a. to reverberate or repeat an original sound after the original sound has stopped
b. to share characteristics or be reminiscent of something
