demonstrator demonstrator /ˈdɛmənˌstreɪtɝ/

noun

1. () A teacher or teacher's assistant who demonstrates the principles that are being taught  ( demonstrator )
   a teacher or teacher's assistant who demonstrates the principles that are being taught
   
2. Someone who participates in a public display of group feeling  ( demonstrator , protester , protestor )
   someone who participates in a public display of group feeling
   
3. Someone who demonstrates an article to a prospective buyer  ( demonstrator , sales demonstrator )
   someone who demonstrates an article to a prospective buyer