It might be clearer to say: According to the dictionary, a squawk is not the same thing as a squeak. there's no need for them to be plural in your sentence and it's likely that, in the dictionary, they're listed as "squeak" and "squawk" singularly. when describing dictionary definitions it's best to use the form of the word that the dictionary uses for clarity.
It is the only line centered around death and the main focus (being the captain) and it's just mostly obvious context clues. Don't stress out the poems, they're easy if you don't think too hard on them.
