1. 忠实的;忠诚的;忠贞不渝的
    Someone who is faithful to a person, organization, idea, or activity remains firm in their belief in them or support for them.

    e.g. She had been faithful to her promise to guard this secret...
           她一直信守承诺，保守着这个秘密。
    e.g. Older Americans are among this country's most faithful voters.
           较年长的美国人是这个国家最忠实的选民群体之一。

2. (对丈夫、妻子或恋人)忠诚的，忠贞的
    Someone who is faithful to their husband, wife, or lover does not have a sexual relationship with anyone else.

faithful什么意思

    e.g. She insisted that she had remained faithful to her husband...
           她坚持说自己对丈夫一直是忠诚的。
    e.g. I'm very faithful when I love someone.
           我爱一个人是会非常忠贞的。

3. (宗教的)忠实信徒，虔诚信徒
    The faithful are the group of people who believe in a particular religion.

    e.g. The faithful revered him then as a prophet.
           那时，信徒们尊他为先知。

4. (叙述、翻译或抄本)如实的，忠实原文的
    A faithful account, translation, or copy of something represents or reproduces the original accurately.

    e.g. Colin Welland's screenplay is faithful to the novel.
           科林·韦兰的电影剧本忠实于原小说。
    e.g. ...faithful copies of household items used in the mid-1800s.
           19世纪中期家庭用品的逼真仿制品

5. (尤指值得信赖的)旧有物品，老牌产品
    You can refer to something that has been used or has existed for a long time as an old faithful, especially when it is something you can rely on.

faithful的意思

    e.g. We tested a selection of vacuum cleaners, from old faithfuls to those with the latest features.
           我们测试了各种真空吸尘器，从值得信赖的老牌子到有着最新特色的产品，不一而足。