demonstrator
UK: ˈdɛmənstreɪtə | US: ˈdɛmənstreɪtər
n. a person who takes part in a public protest or demonstration
n. a device or model used to show how something works
n. (education) a person who teaches by practical demonstration
The word demonstrator traces back to Latin demonstrare, which originally meant "to point out with authority." Over time, it evolved into English, retaining the core idea of "showing" but expanding to include public protests (19th century) and teaching tools (20th century). The suffix -tor consistently marks the doer of the action, creating a clear agentive noun.
The demonstrators marched through the city demanding climate action.
She worked as a science demonstrator at the museum, explaining experiments to visitors.
The company unveiled a new product demonstrator at the trade fair.
Police arrested several demonstrators for blocking the road.
The biology demonstrator prepared slides for the students’ microscope lab.