Buttoned down is an idiom that is often used to describe a person who is cautious and conservative. If you are looking for synonyms for this phrase, then you might consider using words like responsible, reliable, trustworthy, and dependable. These words all have a similar connotation to the idea of being buttoned down because they suggest someone who is careful and thoughtful in their actions. Other potential synonyms for buttoned down might include words like punctual, orderly, organized, and structured. Ultimately, the word you choose will depend on the context in which it is used and the specific meaning you want to convey.