1024: knuckle down Sep 28, 2017

Because language has to rely on multiple people understanding the same references, one of the best way to create new words and phrases is to draw from things many people know. This happens with kennings that draw from mythology, and sometimes jargon, which initially only has meaning for those with a specific occupation, makes its way into common lexicon. The phrase "knuckle down" meaning to apply oneself to a task draws from the game of marbles. In that game, which was once very popular, putting ones knuckles on the taw could help make a better shot.