先生 (xiān sheng) literally combines 先 (xiān), meaning 'before' or 'earlier', and 生 (sheng), meaning 'born' or 'person'. Together, it originally referred to a 'person born earlier' — hence someone senior, learned, or respected. Today, it functions primarily as an honorific title equivalent to 'Mr.' when placed before a surname (e.g., 王先生 — Mr. Wang). It is widely used in formal and polite speech, especially in professional, academic, or service contexts.

Additionally, 先生 can mean 'teacher' in traditional or respectful settings (e.g., addressing a schoolteacher or martial arts master), and historically it was also used for physicians in some regions, though this usage is now rare outside of historical or literary contexts. Unlike Western titles, 先生 is not gender-specific in its etymology but is almost exclusively used for men in modern standard Mandarin; for women, 女士 (nǚshì) or specific professional titles are preferred.