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.
early 15c., "assertion that something is true," from Old French afermacion "confirmation" (14c.), from Latin affirmationem (nominative affirmatio) "an affirmation, solid assurance," noun of action from past-participle stem of affirmare "to make steady; strengthen; confirm," from ad "to" (see ad-) + firmare "strengthen, make firm," from firmus "strong" (see firm (adj.)). In law, as the word for the conscientious objector alternative to oath-taking (Quakers, Moravians, etc.), it is attested from 1690s; if false, it incurs the same penalty as perjury.
c. 1200, "devout, pious, imbued with or expressive of religious devotion," used of Christians, Jews, pagans; also "belonging to a religious order," from Anglo-French religius, Old French religious (12c., Modern French religieux) and directly from Latin religiosus, "pious, devout, reverencing or fearing the gods," also "religiously careful, anxious, or scrupulous," from religio "religious observance; holiness" (see religion).
The meaning "pertaining to religion" is from 1530s. The transferred sense of "scrupulous, exact, conscientious" is recorded from 1590s but restores or revives a sense right at home among the superstitious Romans. As a noun, from c. 1200 as "persons bound by vow to a religious order;" from late 14c. as "pious persons, the devout." Related: Religiousness.
mid-15c., "having or intended to show faith in and reverence for the Supreme Being," from Latin pius "dutiful, devout, conscientious, religious; faithful to kindred; inspired by friendship, prompted by natural affections," perhaps [de Vaan, Klein] related to Latin purus "pure, clean," via a PIE *pu-io- "purifying" (see pure), but the exact development is disputed.
The classical Roman sense of "having or exhibiting due respect and affection for parents and others to whom such is due" is attested in English from 1620s. In the religious sense, sometimes denoting practice under pretense of religion or for good ends (1630s) and in this sense often coupled with fraud (n.). Related: Piously; piousness.
mid-14c., "customary, regular, right, proper;" late 14c., "owed, payable as an obligation, owing by right of circumstance or condition," from Old French deu, past participle of devoir "to owe," from Latin debere "to owe," originally, "keep something away from someone," from de- "away" (see de-) + habere "to have" (from PIE root *ghabh- "to give or receive").
Of actions, "conscientious, careful," late 14c. Meaning "that is to be expected or looked for" is by 1833. Phrase in due time "at a set time; at an appropriate time" is from late 14c. Due to is from early 15c. as "deserved by, merited by;" also "owing to." It is attested from 1660s as "attributable to as a cause or origin." Its use as a prepositional phrase (much maligned by grammarians) is by 1897.