The word "un-important" is a negative adjective that describes something that is not significant or lacking in importance. It is an opposite term of the word "important" which means something that is of great significance or relevance. Some antonyms for the word "un-important" could include words such as "valuable," "essential," "crucial," "critical," "necessary," and "significant." These words indicate that something has a considerable influence or importance in a given context. Choosing the right antonyms for the word "un-important" can help you express yourself accurately and effectively in your writing or speech.