When it comes to describing someone who is truthful and transparent, there are several synonyms you can use in place of "honest aboveboard." For instance, you could describe someone who operates with integrity as "upfront," "sincere," or "forthright." Alternatively, you could describe their behavior as "unambiguous," "straightforward," or "transparent." Similarly, someone who is always honest in their dealings might be described as "fair," "just," or "trustworthy." Ultimately, while "honest aboveboard" is a useful descriptor, there are several other ways to capture the essence of someone who operates with transparency and integrity.