'Protester' definitions:

Definition of 'protester'

From: WordNet
noun
A person who dissents from some established policy [syn: dissenter, dissident, protester, objector, contestant]
noun
Someone who participates in a public display of group feeling [syn: demonstrator, protester]

Definition of 'Protester'

From: GCIDE
  • Protester \Pro*test"er\, n.
  • 1. One who protests; one who utters a solemn declaration. --Shak. [1913 Webster]
  • 2. (Law) One who protests a bill of exchange, or note. [1913 Webster]