An old hand: a person very experienced at doing something

老手：非常善于做某些事的有经验的人

When new employees start at our company, Mary is always the one chosen to train them in the office. She’s an old hand, and we know she can do the job best.

当新员工在我们的公司开始工作，玛丽总是被选出来培训办公室新人的人。她是一个老手，我们知道她可以把工作做的最好。