'thank you
interjection
used to tell someone that you are grateful for something they have given you or done for you
= thanks
　Margaret handed him the butter. 'Thank you,' said Samuel.
　Thank you very much , Brian.
thank you for (doing) sth
　It's good to see you, Mr. Mathias. Thank you for coming.
　Dear Grandma, thank you for the lovely shirt you sent me for Christmas.
used as a polite way of accepting something that someone has offered
　'Can I give you a lift into town?' 'Oh, thank you.'
used when politely answering someone's question
　'How was your trip to Paris?' 'Very nice, thank you.'
no, thank you
used to say politely that you do not want something
　'Would you like some more coffee?' 'No, thank you, I'm fine.'
used at the end of a sentence when telling someone firmly that you do not want their help or advice and are slightly annoyed by it
　I can manage quite well on my own, thank you!

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GRAMMAR
You can use the following expressions to thank someone:
thank you (NOT 'I thank you') : 'Call me if you need anything.' 'Thank you, I will.'
thank you for something : Thank you for the lovely card.
thank you for doing something : Thank you for letting me know (NOT for let me know/that you let me know).
In more informal English, use thanks in the same way : Thanks for the suggestion. | Thanks for helping out.

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