Learner's definition of THANK
to tell (someone) that you are grateful for something that he or she has done or given
I thanked her for (giving me) the present.
I want to thank everyone who helped today.
There's no need to thank me. Anyone would have done the same.
He thanked his grandmother with a big hug. [=he thanked her by hugging her]
have (someone or something) to thank for (something)
— used to say that someone or something is responsible for something
The television show has young audiences to thank for its success. [=the show is successful because it is popular with young audiences]
The city has the mayor to thank [=to blame] for its current fiscal problems.
thank God/goodness/heaven(s)/the Lord
— used to express happiness or relief that something did or did not happen
— used to thank someone
— often + for
— used to politely accept or refuse an offer
“Can I carry that for you?” “Thank you (very much).”
“Would you like another one?” “Yes, thank you.” [=yes, please]
“Can I carry that for you?” “No, thank you. I'll do it myself.”
— used to tell someone in a somewhat annoyed way that you do not want help or advice