The etymology of a word is the historical root from which the word derives. People who study etymologies study the history of words. They gather knowledge about how the word was used in past periods and how it entered other languages. The best way to find this information about a word is a dictionary. When information about the root of a word is available, it is usually included in its dictionary entry.
Elizabeth Coatsworth uses short, quick words in the first stanza of "Swift Things Are Beautiful" because they d. contribute to the ongoing metaphor in Coatsworth's work. In my opinion it's the most correct option.
