Final answer:
The type of parallelism where the same thought is expressed using synonyms is simply known as 'parallelism'. It creates balance in a sentence and is often used to enhance and emphasize the central idea while making the content easier to follow and remember.
Step-by-step explanation:
When the same thought is expressed using synonyms in a sentence, it's a form of parallelism. However, the specific terms provided in the question, such as antithesis, anaphora, parallelism, and synecdoche, each have specific meanings.
Antithesis is the juxtaposition of contrasting ideas, anaphora is the repetition of the same word or phrase at the beginning of successive clauses, and synecdoche is a figure of speech in which a part represents the whole. The correct answer to the question should be parallelism, as it is the broad term that encompasses the repetition of a word or grammatical construction to create symmetry and balance within a text.
As exemplified in President John F. Kennedy's inaugural address, parallelism helps to emphasize an idea and organizes the script with an impactful delivery. This rhetorical device enhances the message and makes it more memorable and pleasing to the listener or reader. Moreover, parallelism is a key component in structuring comparison paragraphs and is often employed in conjunction with other rhetorical strategies like repetition and signpost language to create a coherent and persuasive argument.