noun · a polite title for a man or a way to address a male stranger; Mr. or sir

王先生，这是您的外套。

noun, proper name · a traditional or respectful term for a teacher or a learned person

他是一位德高望重的先生。

noun, particle · a polite way to refer to one's own or someone else's husband

我先生正在出差。

noun · a dialectal term for a physician or medical practitioner

去请那位先生来家里给孩子看病。