Christmas In The Good Old Days
ChatterBank1 min ago
No best answer has yet been selected by Gnisy. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.It means another 'one' - be it person, animal, what ever, dies. The inference is that, in falling over dead, the body has its mouth open, and if it falls face first it literally 'bites the dust' - its teeth will come into contact with the ground.
These days its non-literal use is a pretty unsympathetic description of someone or something who / that has just died.