demonstrator

1. One who demonstrates anything, or proves beyond doubt.
2. The forefinger.
3. One who takes part in a demonstration; a protester.
4. One who demonstrates products in a retail environment; a merchandiser.
5. An item, particularly a vehicle, used in demonstrations to a customer or user.
6. An assistant to a lecturer.
7. One who teaches anatomy from the dissected parts.

الجمع demonstrators