The phrase "most above board" is often used to describe something that is honest, open, and transparent. Antonyms for this phrase could include words like shady, dishonest, sneaky, or underhanded. These are all words that suggest there is something hidden or deceptive happening behind the scenes. Other antonyms could include words like obscure, opaque, covert, or hidden, which suggest that something is not easily visible or understood. Using one of these antonyms in place of "most above board" would drastically change the meaning of the phrase and suggest that something is not trustworthy or straightforward.