Concept:Imaginative comparison between two unlike things is the key poetic device in the given lines.
Explanation:A metaphor directly equates one thing with another without using “like” or “as”.
In the poem, the poet directly calls the dream “a hornbill”.
This is not literally true; the dream is being imaginatively described as a flightless, tottering bird.
Similarly, the dream is called “a locked-up serenade”, another direct comparison.
These expressions are not mere exaggeration, contrast of ideas, or parallel sentence structures.
Therefore, the dominant figure of speech is a metaphor.
Answer:D. Metaphor