protester vs demonstrator

protester and demonstrator both are nouns.

Word	Noun	Adjective	Verb	Adverb
protester	Yes	No	No	No
demonstrator	Yes	No	No	No

As nouns, protester and demonstrator are synonyms defined as:

protester and demonstrator: someone who participates in a public display of group feeling

protester (noun)	demonstrator (noun)
someone who participates in a public display of group feeling	someone who participates in a public display of group feeling
a person who dissents from some established policy	someone who demonstrates an article to a prospective buyer
	a teacher or teacher's assistant who demonstrates the principles that are being taught