In-appurtenant is a term used to describe something that is not relevant or related to a particular situation or topic. Its antonyms, however, refer to words that describe something that is relevant, important, or pertinent. These antonyms include relevant, significant, applicable, suitable, appropriate, and related. While the term in-appurtenant implies a lack of importance or relevance, its antonyms connote a sense of importance, relevance, and value. It is important to use the appropriate antonym when trying to convey the exact meaning you intend and avoid any unintended confusion or miscommunication in your writing.