The word un-buckle means to undo or release a buckle, and its antonyms are words that mean the opposite. Some antonyms for un-buckle include fasten, buckle up, secure, and latch. When you fasten or secure something, you do the opposite of un-buckle, which is to make sure that a buckle stays in place. Buckle up means to fasten your seat belt, which is the opposite of un-buckle your belt. Finally, latch refers to the process of joining two things together securely, and is an antonym for un-buckle because it involves making sure that something stays in place. Overall, these words represent the opposite of what un-buckle represents, and highlight the importance of keeping things securely fastened.