Learner's definition of PACIFIST. [count]. : someone who believes that war and violence are wrong and who refuses to participate in or support a war. A group of pacifists were protesting the war. [+] more examples [-] hide examples [+] Example sentences [-] Hide examples.adjective, always used before a noun. someone who believes that war and violence are wrong and who refuses to participate in or support a war. A group of pacifists were protesting the war.