The dining table was a plain board called by that name. It was hung on the wall when not in use, and was perched on the diners' knees when food was served. Over time, the word board came to signify not just the dining surface but the meal itself, which is where the board comes from in room and board. It also explains why lodgers are called boarders.
( Bill Bryson )
[ At Home: A Short History of ]
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