Moved up and down in a quick, bouncy manner; or cut hair short in a bob style (especially popular in the 1920s).
From bob, a verb with multiple related meanings. The primary sense comes from Middle English bobben, likely imitative of bouncing motion. The hair-cutting sense developed in the 20th century when the 'bob' hairstyle became fashionable. Both senses share the idea of quick, rhythmic movement.
The bob haircut of the 1920s was genuinely rebellious—women cutting off their long hair was considered shocking, and 'bobbed' became the word for women breaking free from traditional expectations!
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