A teacher or teacher's assistant who demonstrates the principles that are being taught.

Roget 524: interpreter; expositor, expounder, exponent, explainer; demonstrator.    scholiast, commentator, annotator; metaphrast^†, paraphrast^†; glossarist^†, prolocutor.    spokesman, speaker, mouthpiece.    dragoman, courier, valet de place, cicerone, showman; oneirocritic^†; (Edipus; oracle) &c.. 513 ... show more

Someone who demonstrates an article to a prospective buyer.

synonym: sales demonstrator.

Someone who participates in a public display of group feeling.

synonym: protester.

Dutch: betoger, demonstrant, manifestant
Polish: demonstrant, manifestant