Antonyms for the phrase "are an adjunct" include absolute, autonomous, independent, pure, and self-sufficient. While "are an adjunct" suggests dependency or a relation to something else, these antonyms imply a sense of self-contained nature or completeness. For instance, an autonomous system operates independently, while a pure substance is uncontaminated and unadulterated. Using antonyms like these can be helpful when writing to emphasize the contrast between the qualities of the original phrase, especially when describing a situation that calls for self-sufficiency or independence.