board: [OE] Old English bord had a wide range of meanings, whose two main strands (‘plank’ and ‘border, side of a ship’) reveal that it came from two distinct sources: Germanic *bortham and *borthaz respectively (despite their similarity, they have not been shown to be the same word). Related forms in other Germanic languages that point up the dichotomy are Dutch bord ‘shelf’ and boord ‘border, side of a ship’.
The second, ‘edge’ element of board (which is probably related to border) now survives in English only in seaboard (literally the ‘edge of the sea’) and in variations on the phrase on board ship (whose original reference to the ship’s sides is nowadays perceived as relating to the deck). Board ‘food’ (as in ‘board and lodging’), and hence boarder, are metaphorical applications of board ‘table’. => border
