The noun “hope” serves as a combination of “desire” and “expectation.” It captures those feelings that we do more than dream of: we want to believe that they will happen. Hope, then, is far less abstract; it represents an actual desire to better one’s self, position, relationships, or environment.
When a noun is first introduced, English speakers often use the indefinite article, “a” or “an,” before the noun. This signals that it is one of many and allows the speaker to define it momentarily. Dickinson’s speaker instead uses the definite article, “the,” here to clearly state that hope is the only thing that can perform these functions. This not only strengthens the speaker’s claim, but it also sharpens the focus of the work.
The noun “extremity” means the limit or terminal point, indicating in this case a condition of extreme urgency or need. It refers back to the superlative descriptions of “sea” and “land” and suggests that even in the worst of conditions the bird does not ask anything of the speaker. It is the perfect companion for hardship.
“Chillest” and “strangest” are superlatives. Superlatives are words used to note the highest quality or degree of something. In using these hyperbolic words, the speaker suggests that the little bird and the hope it brings survives through the worst conditions.
The verb “abash” means to cause someone to lose self-possession or confidence as a result of shame or humiliation. The speaker acknowledges the possibility that a storm could cause the little bird to lose itself and stop singing. Notice however that the speaker characterizes the storm that could do this as “sore,” extremely severe, harsh, or serious, and qualifies this ability with the conditional “could.” This indicates that even if there were such a storm that could “abash” the little bird, it is rare.
A “gale” is a strong wind and is generally used to refer to storms that occur out on the ocean. Metaphorically, this gale represents a dark, challenging, or terrifying moment in someone’s life. The speaker recognizes that the little bird’s song of hope is most comforting during these times of peril, even though it sings all the time.