当代词语里，老实有傻的意思。而且不具任何色彩。 忠实有忠诚的意思，这个词要有目标，比如，我是他忠实的粉丝。意思是我对他忠实，表现为不轻易更改忠实对象。 诚实和老实有区别，聪明的老实就是诚实，诚实主要表现为不说谎。老实主要表现为不讹人。一个言语，一个行为。 真挚是个形容词，和其他几个词语不具有可比性，译为real，一般指感情真挚。 诚恳有恳求的意思，我诚恳地看着他，基本上我也会同时希望他答应我一些事，真诚地有求于人，叫诚恳

老实 is to describe that a person is very kindly. He never sets up someone. He never breaks any rule and law. He always believes other people. When someone is too 老实, he can't distinguish any lie. In this case, 老实 is a bad word, meaning someone is fool because he always believes other people. It seems that he has no brain. 诚实 means "no lie". 他是个诚实的孩子 means he is a child never lying. 忠实 means faithful. For example, 我是巴西队忠实的球迷(faithful fan). 这名法官忠实地执行了宪法。 This judge follow out the constitution faithfully. 诚恳 means a kind of believable feeling. When someone does something or says something that makes you feel that he doesn't lie, you can use 诚恳. For example, 他诚恳地向我道歉. He says sorry to me and I can feel that he really wants to say sorry to me. 真挚 is about emotion, such as 友情、爱情. It means that the emotion is true. For example, 他们一起经历了各种磨难，他们的爱情一定是真挚的。

首先解释忠实，百度给的解释是"忠诚老实"，我个人的理解它区别于其他词是多了一层敬仰、追随的意思，就像上个回答 :忠实粉丝。 诚实，多用于形容一个人的性格或者品德，一般翻译习惯和honest一个意思。 真挚，用于形容人的情感，真诚而确切。 诚恳，多用于表示态度。 老实，形容一个人的个性或者给人一种感觉，像脚踏实地、不说谎的人。比如有人的就被称为:老实人。

谢谢大家的评论。看完以后，我清楚多了。