The antonyms for the word "un-justifiable" include the words "justifiable," "reasonable," and "valid." These words describe situations where there is a legitimate reason or explanation for something. Justifiable means that there is a good enough reason or excuse to justify the action. Reasonable means that something is sensible, logical, or fair. Valid means that something is legally or officially acceptable. These antonyms can be used to express legitimate reasons for actions or decisions, such as a justifiable use of force or a valid legal claim. Using these antonyms can help to clarify a situation and provide understanding of why something was done.