welcome

First recorded before 900; Middle English, from Scandinavian; compare Old Norse velkominn, equivalent to vel well¹ + kominn come (past participle); replacing Old English wilcuma “one who is welcome,” equivalent to wil- welcome (see will²) + cuma “comer”

The seemingly timeless phrase “You are welcome” —usually shortened to “You're welcome” —as a response to “Thank you” is actually quite recent. The phrase does not appear to have been used with any regularity until the 19th century. By the early 20th century, however, it was well established in the United States (less so in Britain) as the customary and polite way to acknowledge thanks for a favor or service, recommended in etiquette guides and taught to children along with “Please” and “Thank you.”
But the phrase “You're welcome" has always existed alongside a host of other possible responses to a thank-you, ranging from a casual “Sure” or “Any time” to more elaborate expressions like “You're quite welcome” or “My pleasure; I'm happy to help.” There is even a reciprocal thank-you: Thank you for coming to my party. Thank you for inviting me. Toward the end of the 20th century, especially among younger people and in very informal situations, it became popular to respond with a breezy “No problem”— a phrase that, though well received in some situations, can come across as flippant and dismissive of the other person's expression of gratitude. Many different forms of expression can be appropriate for acknowledging thanks for a favor or service in different circumstances; but among the varied expressions, the one that is always gracious remains the classic “You're welcome.”

C12: changed (through influence of well 1) from Old English wilcuma (agent noun referring to a welcome guest), wilcume (a greeting of welcome), from wil will ² + cuman to come