Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
1896, in reference to those with religious scruples about mandatory vaccination. Military sense predominated from World War I.\n\nAfter a chequered career full of startling episodes and reversals, the Vaccination Bill becomes virtually the Vaccination Act. In Parliament the hottest of the contest centred round the conscientious objector.
[The Lancet, Aug. 13, 1898]
Wiktionary
n. Someone who refuses to fight in an armed conflict because of religious or moral principles.
WordNet
n. one who refuses to serve in the armed forces on grounds of conscience [syn: CO]
Wikipedia
A conscientious objector is an "individual who has claimed the right to refuse to perform military service" on the grounds of freedom of thought, conscience, disability or religion. In general, conscientious objector status is considered only in the context of military conscription and is not applicable to volunteer military forces.
In some countries, conscientious objectors are assigned to an alternative civilian service as a substitute for conscription or military service. Some conscientious objectors consider themselves pacifist, non-interventionist, non-resistant, non-aggressionist, or antimilitarist.
On March 8, 1995 the United Nations Commission on Human Rights resolution 1995/83 stated that "persons performing military service should not be excluded from the right to have conscientious objections to military service." This was re-affirmed in 1998, when resolution 1998/77 recognized that "persons [already] performing military service may develop conscientious objections.". A number of organizations around the world celebrate the principle on May 15 as International Conscientious Objectors Day. The term has also been extended to objecting to working for the military-industrial complex due to a crisis of conscience.
Usage examples of "conscientious objector".
Fifteen minutes later Herbie Goldfarb, pacifist, conscientious objector, VISTA volunteer, walked out of there like a young man who had just lost his virginity, the gun and a box of bullets tucked down snug in his pack among the corned beef hash and Spam cans, peanut butter, Bunny bread, and beer.
Even the most fervent and naive conscientious objector knew the answer to that one.
For some moments he had been muttering to himself, and it had been plain that he was not in sympathy with the conscientious objector.
Though only fourteen at this time, a weedy-lanky boy with a cracking voice, Patrick was an admirer of the war-protesting Berrigan priest-brothers and warned he'd run away to Canada as a conscientious objector if necessary.
With sudden clarity he realized that he was annoyed with the role assigned to him, that of the privileged noncombatant, the excused conscientious objector.