What about Owl-Eyes who acts as the enhancement to the occular imagery in F. Scott Fitzgerald's "The Great Gatsby"?
Having no real name, this character of synedoche acts as the eyes that perceive the truth about Gatsby. For instance, when he is in the library at Gatsby's house during a party, he is surprised that the books are real and bound in real leather with actual pages; he has suspected that they, like Gatsby, would merely have the appearance of being genuine. Also, in the last chapter, Owl Eyes is the only one of the party group to attend the funeral for Gatsby because, as he come "splashing" after Nick and Mr. Gatz, he wants to meet the father and learn more about Jay Gatsby. When he talks to Nick after the funeral, he remarks,
'I couldn't get to the house.'
'Neither could anybody else.'
'Go on'...Why my God! they used to go there by the hundreds.'
He took off his glasses and wiped them again outside and in. 'The poor son-of-a-bitch,' he said.
Like the billboard that sits overlooking the Valley of Ashes, Owl Eyes sees and understands all.
A synecdoche is a figure of speech. Synecdoche is a literary term which through metaphor or rhetorical device is used to express either more, or less, than it literally denotes. It is used when a whole is used as the part or a part of a thing is put for the whole.
Fitzgerald used a lot of different types of literary terms in his writing and synecdoche is just one type. You can find examples throughout the novel once you get the hang of it. On Nick’s first visit to Tom and Daisy Buchanan’s’ house, Tom explains to Nick that the house previously belonged to “Demaine the oil man.” (pg.12) This term is used to describe Mr. Demaine as a man who had made his fortune in the business of selling and buying crude oils. Later in that same chapter Nick is described as a “bonds man,” which indicates that he sells stocks and bonds for a living. On page 138, near the middle of chapter 7, Nick is trying to explain that Daisy loves him and most importantly that he loves her. Nick states: “Once in a while I go off on a spree and make a fool of myself.” (pg138) By using the term “spree” Nick is saying that he is being unfaithful and rather than saying he commits adultery or cheats on his wife he uses the term “spree.”
"Synecdoche is closely related to metonymy (the figure of speech in which a term denoting one thing is used to refer to a related thing); indeed, synecdoche is sometimes considered a subclass of metonymy. It is more distantly related to other figures of speech, such as metaphor."
Synecdoche is a literary device in which an author uses a part of a thing as a metaphor for the whole thing. It can also work the other way -- it can use the whole as a metaphor for the part of the thing. More generally, it can be done by using the word for a class of things to refer to a specific thing in that class (you sometimes see someone refer to their car as "my machine" in old books).
In The Great Gatsby, you can see this device as soon as the first page or two of the book. Carraway, for example, talks about how he "enjoyed the counter-raid" as a way of saying he enjoyed the excitement of war.
A bit later on in the first chapter, Carraway is describing Tom Buchanan and says that some people at Yale hated Tom's guts. This is an example of synechdoche because Tom's guts are being used as a metaphor for the whole person.
Fitzgerald's dominant trope in the novel is centered around synecdoche.
Geographically: East Egg is representative of the East Coast. West Egg is representative of the West Coast. The Valley of Ashes is representative of the Middle West.
Character: Daisy is representative of the generation of "hopeless little fools" whose voices are "full of money." They say a lot but mean nothing.
Objects: the cars are representative of the materialism and destructive forces of society. The wheels come off them during the party. Daisy runs over Myrtle. George works on Tom's car, while Tom whisks his wife off to their NY apartment.