faithful, upstanding

誠(まこと) Faithfulness and fidelity to your boss or superior person.
 
誠実(せいじつ) Fidelity to your lover. (used as noun or na-adjective)
 
正直(しょうじき) Integrity in your dealings with everyone.   $$$
 
堅実(けんじつ) Reliability. 堅実 doesn’t have the moral aspect of words like 誠 or 誠実. 堅実 is more like, someone who works steadily, who doesn’t take chances, who is always on time, who is rock-solid and conservative.
 
忠実(ちゅうじつ) Someone who is faithful in doing his/her duties. Also means like a movie which is faithful to the book, or a translation which is faithful to the original. Or even a forgery which copies the original dollar bill completely well.