Guided by or in accordance with the dictates of conscience; principled: a conscientious decision to speak out about injustice.
Thorough and assiduous: a conscientious worker; a conscientious effort to comply with the regulations.
[Obsolete French conscientieux, from Medieval Latin cōnscientiōsus, from Latin cōnscientia, conscience; see conscience.] con'sci·en'tious·ly adv., con'sci·en'tious·ness n.