誠に[makotoni] indeed
誠意[seii] sincerity
誠実[seijitsu] sincere
誠心誠意[seishinseii] in all sincerity
丹誠[tansei] working earnestly

忠誠[chuusei] loyalty
不誠意[fuseii] insincerity
不誠実[fuseijitsu] insincerity
至誠[shisei] sincerity