The phrase "art up and up" refers to something that is ethical, honest, and legitimate. When looking for synonyms for this phrase, you can use terms like "aboveboard," "legit," "genuine," "lawful," and "ethical." Other options include "credible," "authentic," "kosher," "straightforward," "trustworthy," and "principled." These words are often used to communicate that something is not fraudulent or deceitful and is operating within the guidelines of moral and legal parameters. Using these synonyms can help enhance the clarity and accuracy of your communications and ensure that your audience understands your message correctly.