board has 17 distinct synonyms spread across 9 of its 13 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a committee having supervisory powers
“the board has seven members”
a flat piece of material designed for a special purpose
“he nailed boards across the windows”
food or meals in general
“she sets a fine table”
a vertical surface on which information can be displayed to public view
electrical device consisting of a flat insulated surface that contains switches and dials and meters for controlling other electrical devices
“he checked the instrument panel”
a printed circuit that can be inserted into expansion slots in a computer to increase the computer's capabilities
a flat portable surface (usually rectangular) designed for board games
“he got out the board and set up the pieces”
live and take one's meals at or in
“she rooms in an old boarding house”
Synonyms, antonyms and the broader and narrower relations for board come from Princeton University’s WordNet. Full sources and licences.