先生

In Chinese, a title sits in front of the name, not behind it. So 王先生 reads as Mr. Wang, never Mr. of Wang. Flip the position, put 先生 after 我, 她, or 你, and it hard-switches to 'husband' or 'sir.' Position, not extra words, is what does the disambiguating. A name in front means a title; a possessive in front means a husband.

先生 is loaded with 'male adult' the same way 'Mr.' is in English. Some classical writing honored a great female scholar as 先生, but that's a dusty exception, not a rule. If you call your female boss 先生, it lands as a gender mistake, not politeness. Use 女士 as the direct counterpart to 先生, or 老师 for teachers of any gender.

For centuries, the person standing across from a 学生 was addressed as 先生. That pairing still shows up in set phrases and old texts, which is why learners second-guess it. But daily Mandarin reserves 老师 for teachers and keeps 先生 for 'Mr., sir, husband.' Read 先生 as 'teacher' only in classical or deliberately old-fashioned writing.

“女士和男士，男生和女生，先生和学生。” (Ladies and gentlemen, boys and girls, Mr. and student.)

In 先生, the second syllable drops its full first tone and squashes into a quick neutral tone. Pronounce it as a heavy xiānshēng and you sound like a dictionary reader. The same crush happens in 学生 (xuésheng) and 医生 (yīsheng), so treat it as a pattern, not a one-off.