“I'll make it. ...I must have done it a hundred times. I could whip up a Mandrake Restorative Draught in my sleep —”
“Excuse me ...But I believe I am the Potions Master at this school.”
-- Severus Snape to Gilderoy Lockhart (CS9)
The potions professor at Hogwarts is the Potions Master, therefore it is a job title that goes with the position.
- Severus Snape was Potions Master during the first five years of Harry's schooling at Hogwarts. In sixth year, he switched to Defense Against the Dark Arts professor and Horace Slughorn took over the position, which he had previously held when Snape and Harry's parents were in school (HBP8). In seventh year, Snape became Headmaster of Hogwarts, and Slughorn remained as Potions Master (DH12).
- The Potions Master teaches in the potions dungeon under the school and has an office nearby (PS8).
- Both Snape and Slughorn also worked as Head of Slytherin House, but there may have been Potions Masters in history with other House affiliations.
- Early Potioneer Zygmunt Budge called himself a Potions Master in his Book of Potions because he believed he was passing on his brilliance to the next generation. (Although he admitted he left Hogwarts at 14 and never graduated, nor taught there.) (BoP)
"master" from late Old English mægester "one having control or authority," from Latin magister (n.) "chief, head, director, teacher"