What does "hire" mean here? Is it a noun?
Used in this context, "(new) hire" is a noun meaning new employee. This term is casual and can be used to describe any new employee. Ex: Have you met the new hire yet? I heard she's starting work today. Ex: We have a few new hires who've been assigned to the marketing department. You can also use the term "old hire" to refer to an employee who was hired a long time ago. Ex: A: Who's that, is he a new employee? B: Joe? Nah, he's an old hire.