Let's first define what constitutes a "rhetorical device."
The Guide to Literary Terms by eNotes has an ample index with all the information you need to best understand how authors use their craft.
In the guide, the definition of "rhetoric" reads:
..the theory and principles concerned with the effective use of language or the theory and practice of eloquence, both written and oral. It consists of the rules that govern all prose composition or speech designed to influence the judgment or feelings of people
This said, a rhetorical device is a product rhetorical language. It is the use of words to cause a reaction, or make an effect, in the audience. This effect does not have to be some colossal reaction. Instead, rhetorical language effectively engages the imagination in a way that the reader can see and feel exactly (or close to) what the author sees and feels.
When reading Ethan Frome, the reader can feel sensations and create visuals that may or may not be part of their own life experiences....
(The entire section contains 3 answers and 1369 words.)