Irredundant is a word that refers to something that is not repetitious or unnecessary. Synonyms for this word include essential, indispensable, critical, and crucial. Other words with similar meanings include necessary, important, vital, and paramount. When something is irredundant, it means that it is so important or crucial that it cannot be removed or replaced without negatively impacting the overall outcome. It could also mean that the item or idea in question is unique or inimitable, and therefore cannot be duplicated or substituted with anything else. Whatever the context, the synonyms for irredundant all imply a high level of importance or indispensability.