Aboveboard, adv.
Above the board or table. Hence: in open sight; without trick, concealment, or deception. "Fair and aboveboard." Burke.
Note: This expression is said by Johnson to have been borrowed from gamesters, who, when they change their cards, put their hands under the table.
Shades of meaning
Fernald has no entry of its own for aboveboard; he lists it under candid.
He lists it without comment; the entries above explain its neighbors.