General:
* Panel
* Plank
* Surface
* Platform
* Deck
* Sheet
For a governing body:
* Committee
* Council
* Trustees
* Directors
* Management
For a meal:
* Meal
* Supper
* Dinner
* Feast
For getting on a train/bus/ship:
* Embark
* Enter
* Get on
* Go aboard
For a game:
* Game piece
* Tile
* Piece
* Counter
Please provide more context about how you're using the word "board" so I can give you a more specific synonym.