诚意 (chéng yì) means sincerity in a formal or transactional sense — good faith in negotiations, agreements, or mutual dealings. It differs from 真心 (zhēn xīn), which is personal genuine feelings for someone, and 心意 (xīn yì), which often refers to a thoughtful gesture or gift (一点心意). 好意 (hǎo yì) is simply good intentions, while 忠心 (zhōng xīn) is loyalty to a person or cause.