thanks：n. 谢谢（只用复数）int. 谢谢Thanks for your help when I was in trouble.谢谢你在我困难的时候帮助我。

thankness：n. 感激I can't use any word to express my thankness.我无法以语言表达我的感激之情。Again, I don't know how to express my thankness.还有，我觉得应给你加双倍的分。I cannot use any words to express my thankness.我无法以语言表达我的感激之情。It not enough by any words to express my thankness.我的感激之情并非言辞所能表达。

Thank本身是名词,也是动词，thank you最常用 ，是动词用法，但如果thank用作名词也可以，可以说many thanks，就表示I want to give you many thanks,是口语化用法

而thankness也是名词,表示感谢的这种状态，因为ness是名词后缀的时候，他就描述的是一种状态。