The word "magister" means someone who is a teacher or an expert in a particular field. It refers to a person who has knowledge and authority in a specific subject. Full definition
The large Dungeness crab (Metacarcinus magister) is an important source of income for fishermen along the west coast of North America from Alaska to California. (sciencedaily.com)
Dungeness Crabs (Cancer magister) Born in the open ocean, millions of crab larvae drift into the bay. (parksconservancy.org)
However, this reviewer would also have appreciated a morning collation with Thomas the magister sacrae paginae, showing the Scriptural and liturgical matrix of the Church's doctrine. (firstthings.com)