1 scrupulous, principled, fair, moral, ethical, strict, righteous, right-minded, upstanding, upright, honourable, just, responsible, high-minded; incorruptible:
Fetherby is a conscientious arbitrator.
2 cautious, careful, scrupulous, exacting, meticulous, punctilious, painstaking, diligent, particular, rigorous, thorough:
A conscientious effort was made to restore the painting to its original condition.
3 prudent, discreet, politic, careful, circumspect, heedful, attentive, serious:
Fred is conscientious about keeping secrets.