Large pellets fired from a shotgun, or a scattering of something in many directions.
From 'buck' (a male deer) plus 'shot.' Originally called 'buckshot' because it was large enough to hunt bucks, distinguished from smaller birdshot used for birds.
The progression of shotgun ammunition is poetic: birdshot for birds, buckshot for bucks (deer), and slugs for larger game—it's literally named by what animal you're hunting, which tells you exactly what each one does.
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