大师(dà shī) - master, grand master in Mandarin

大师 (dà shī) is a title, not a job. It marks someone whose command of a craft is so complete that the craft itself is associated with them: a calligraphy 大师, a chess 大师, a chef who has earned the word. The measure word is 位 (wèi), the polite one, because using 个 with it sounds off.

It began as a Buddhist honorific for a senior monk and still carries that weight. That is why it also gets used sarcastically. Call an amateur a 大师 with the wrong tone of voice and you have insulted him.

The trap is reaching for it as a translation of "master" in the everyday senses. A postgraduate master's degree is 硕士 (shuò shì), a master craftsman you employ is 师傅 (shī fu), and the master of a house is 主人 (zhǔ rén). 大师 is reserved for genuine eminence, so it sounds absurd applied to an ordinary skilled person.