Moves up and down with short, quick movements, or the plural of bob (a hairstyle or a device that bobs).
From Middle English 'bobben,' possibly imitative of the motion itself. The word has been used since the 1300s to describe bouncing or nodding movements, and later adopted for the bob hairstyle (shortened from 'bobbed hair') popular in the 1920s.
When the bob haircut became fashionable in the 1920s, it was absolutely radical—women's hair had been long and pinned up for centuries, so 'bobbing' your hair was a rebellious statement that became synonymous with the modern, liberated 'flapper,' making the hairstyle name carry social revolution within it.
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