When you want to refer to something that is not the main object of your discussion or focus, there are several synonyms that you can use. Some of the most common options include secondary, peripheral, incidental, subordinate, minor, auxiliary, and supplementary. Using one of these synonyms can help to clarify your meaning and make your writing more precise and nuanced. For example, instead of saying "The book is not the main focus of the article," you could say "The book is secondary to the primary argument of the article." Whether you are writing an academic paper, a blog post, or a casual email, choosing the right synonyms can make your writing more effective and engaging.