Synecdoche (pronounced sin-ek-de-key) is a figure by which one word receives something from another which is internally associated with it by the connection of two ideas: as when a part of a thing is put by a kind of Metonymy for the whole of it, or the whole for a part. The difference between Metonymy (covered two weeks ago) and Synecdoche lies in this: that in Metonymy, the exchange is made between two related nouns; while in Synecdoche the exchange is made between two associated ideas.
John 3:16 is a great example of Synecdoche. “For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life.” What is meant by the word “world” in this verse? Did God give His son to die for the plants and animals, for the trees and the mountains? No. God gave His son to die for mankind. Synecdoche replaced one idea (world), with another (mankind). This figure of speech is used for multiple reasons. One reason it is used here is to show the entirety and completeness of the work Jesus preformed.
We must also note Acts 20:7: “On the first day of the week, when we were gathered together to break bread, Paul began talking to them, intending to leave the next day, and he prolonged his message until midnight.” These Christians came together to “break bread,” meaning that their purpose for gathering was to partake of the Lord ’s Supper. Breaking bread is a part of communion but not the whole part. This breaking of bread was not a common meal because it was done specifically on the first day of the week, it was the reason for gathering, and a common meal is mentioned only four verses later.