Diction refers to the specific word choices an author makes, and a writer's choices of words can help portray theme, style, and even tone. A theme is the subject matter that a piece of literature is about; style, particularly a writer's style, refers to the way in which an author describes "events, objects, and ideas" ("Defining Style"); and tone refers to the writer's attitude concerning the subject matter ("Tone vs. Mood"). The diction, meaning word choices, syntax, and other literary devices all come together to convey the writer's images, story, and ideas. Dr. Wheeler gives a good example of diction when he points out that a writer can choose to call a "rock formation" by a number of words, including "a stone, a boulder, an outcropping, a pile of rocks, a cairn, a mound, or even an 'anomalous geological feature'" (Dr. Wheeler, "Literary Terms and Definitions: D"). Each of these terms have different connotations, create different images in the reader's head, and help to portray a completely different attitude. Any piece of literature, especially Shakespeare's Romeo and Juliet, is full of different diction choices, and all you have to do is choose a particular scene or speech to analyze in order to zero in on the word choices and see exactly what Shakespeare is conveying through the word choices. Using a dictionary will help you with this project, even for words you are already familiar with, because a dictionary will help you see connotations you are unaware of, which can help you better see Shakespeare's possible intentions in the diction choices.
Let's take Prince Escalus's speech in the opening scene as an example. Even the very first line is full of word choices that convey interesting meaning. The word "subject" is an interesting choice of diction because the word subject can refer to people who are ruled by a king or government, but it can also refer to a dominant theme (I.i.77; Collins English Dictionary). Hence this one word "subject" addressed to the warring Montagues and Capulets shows us that, not only should they be under Prince Escalus's rule but are failing to do so out of rebellion, but also that the feud between the Montagues and Capulets, especially their unrelenting, unfounded hatred for each other, is the central theme of the play. The word "enemies" is also an interesting word choice because, not only does it refer to hostile groups of people, it first refers to people who hate each other and act in ways to harm each other, which is a perfect portrayal of the Capulets and Mongtagues (77; Random House Dictionary). In addition, the diction choice for the phrase "enemies to peace" is also very interesting because, not only does the term peace juxtapose the word enemies, the entire phrase further portrays Shakespeare's message that the Montagues and Capulets are not just enemies to each other, they are enemies of harmony, friendship, lawfulness, and order, meaning that they hate all of these things (77).