Conscientious
early 17th century: from French consciencieux, from medieval Latin conscientiosus, from Latin conscientia (see conscience).
wiktionary
From Middle French conscientieux, from Medieval Latin cōnscientiōsus.
etymonline
conscientious (adj.)
1610s, of persons, "controlled by conscience, governed by the known rules of right and wrong;" of conduct, etc., "regulated by conscience," 1630s, from French conscientieux (16c.; Modern French consciencieux), from Medieval Latin conscientiosus, from Latin conscientia "sense of right, moral sense" (see conscience). Related: Conscientiously; conscientiousness.
Conscientious objector is from 1896, in reference to those with religious scruples about mandatory vaccination. Military sense predominated from World War I.
After 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]
Slang shortening conchy is attested from 1917.
