A person who shows how something works or explains something by displaying it, or a person who participates in a public protest.
From Latin demonstrator, derived from demonstrare (to show/point out). The -or suffix denotes an agent noun (one who performs the action). The word gained the protest meaning in the 19th century.
The same word covers both the person showing off a new blender at the mall AND the activist marching down the street—because both are 'showing' something, one showing how a product works and one showing their beliefs!
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