If you want to have a good result in Chinese studying, you need to recognize some synonyms.
You may hear Chinese people call a teacher “先生” in a university. But you will never hear a person do such introduction to his teacher.
“这是我先生”(zhè shì wǒ xiān shēng). This sentence is not the meaning of “This is my teacher” or “This is my professor”. In fact, it means “This is my husband”.
“先生”(xiān shēng) has three meanings in Chinese. The first one is an appellation only for the teachers who have a higher level of knowledge. In this situation, “先生” has the same meaning as “老师”(lǎo shì)—teacher.
For example, “王先生教我们汉语” (wáng xiān shēng jiāo wǒ mēn hàn yǔ)—–Teacher Wang teaches us Chinese.
The second meaning is the appellation of sir on social occasions. We call gentlemen “先生”, similar to appellations of ladies”女士”(nǚ shì) or “小姐”(xiǎo jiě).
Last but not least, “先生” can also be used to describe husband. There is always a pronoun before “先生”.
EX: 他是我先生(tā shì wǒ xiān shēng)——He is my husband.
你先生在哪儿工作？(nǐ xiān shēng zài nǎ ér gōng zuò)—–Where does your husband work?
So if you want to introduce your teacher to sb. Pls, remember to use the correct sentence. “这是我的老师,王先生”(zhè shì wǒ de lǎo shī wáng xiān shēng)