What does 'bite the dust' mean?

bite the dust

Suffer defeat or death, as in The 1990 election saw both of our senators bite the dust. Although this expression was popularized by American Western films of the 1930s, in which either cowboys or Indians were thrown from their horses to the dusty ground, it originated much earlier. Tobias Smollett had it in Gil Blas (1750): "We made two of them bite the dust."