The word "thank" has several meanings, depending on its context.
1) As a verb, to thank means to express gratitude or appreciation for something done by another person. For example, one might say "I want to thank my friend for helping me with the project."
2) As an adjective, thank can refer to something that is pleasing or satisfying. For instance, you could describe a delicious meal as "a really thank dinner".
3) In some English dialects, particularly in Scotland and Ireland, "thank" means "to nod in agreement."