It's a noun/interjection when used in the most common form, similar to, "yes" or "ouch!"
When used in this way: "I thank you for your time," it becomes the verb and direct object of a clause.
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adverb
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The phrase "thank you" is an interjection. It is commonly used to express gratitude or appreciation in response to something.
like this example mother it became a mo-ther that the answer thank you
thank you
yes
thank you for listening, i hoped you enjoyed, i hope you found my speech...
of course we can use it
thank you for loving me
part of speech
The part of speech for this particular word is a noun.
adverb
what part of speech is work
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