When something becomes permanent, it means that it has become long-lasting or irrevocable. Here are some synonyms that can be used in place of "become permanent." Firstly, "solidify" can be used when something becomes permanent, like a relationship or agreement, and is not easily changed. Secondly, the phrase "set in stone" can be used to describe something that has become permanent, like a decision or plan. Thirdly, "irreversible" can be used to describe something that cannot be changed, like a medical condition or legal ruling. Lastly, "indelible" can be used to describe something that has left a permanent impression or mark, like a memory or scar.