What literary device refers to using a part to refer to a whole, as in saying "America" instead of "USA"?

The literary device being described is indeed synonymous with using a part to refer to a whole, and your choice of synecdoche aligns perfectly with that definition. Synecdoche is a figure of speech in which a part of something is used to represent the whole entity, or vice versa. In the example given, "America" is used to refer to the entire nation, the USA. This device not only creates a more vivid image but also allows for concise expression, as it encapsulates a broader concept within a single word.

While metonymy, which could seem similar, involves substituting a related term for the thing itself (like using "the White House" to refer to the U.S. President and their administration), synecdoche specifically involves a direct part-whole relationship. Alliteration pertains to the repetition of consonant sounds at the beginning of words, and personification attributes human characteristics to non-human entities. Therefore, synecdoche is the most fitting choice in this context, illustrating how language can be both economical and evocative in expression.