magist-, master- +

(Latin: magister, chief, head, leader; from Latin magnus, "great")

masterpiece
1. An outstanding achievement.
2. The most outstanding work of a creative artist or craftsman.
3. An exceptionally good piece of creative work; for example, a book, movie, or performance.
mastery
1. Expert knowledge or outstanding ability.
2. Having total control over someone or something.
3. Full command of a subject of study.
mistress
1. A woman with whom a man has a usually long-term extramarital sexual relationship, often one in which he provides financial support.
2. A woman who owns or controls something.
3. Something that rules or controls something or someone; personified as a woman.
4. A woman who is highly skilled in a particular activity.
postmaster (s) (noun), postmasters (pl)
1. The person who is in charge of an independent agency that is responsible for the delivery of correspondence to people and to businesses: The postmaster is responsible for making sure that mail personnel arrange for the delivery of letters and packages and that they are actually taken to those who are supposed to receive them.
2. The person responsible for the maintenance of a website and for being the contact point for information and complaints: Brad and his wife Alice were the postmasters for several web sites and responded to incoming mail promptly.
3. A computer e-mail program that distributes, forwards, and receives electronic mail: The computer had an efficient program to function as the postmaster of the electronic messages and services it was providing.
whoremaster
1. A man who associates with or pays for sexual relations with prostitutes or a prostitute.
2. Someone who consorts with whores; a lecher or pander.
3. A pimp who procures whores for customers; usually, a man, who finds customers for a prostitute in return for a portion of the prostitute's earnings.

Cross references of word families related directly, or indirectly, to: "master, lead, leading, ruler, ruling, govern": -agogic; agon-; arch-; -crat; dom-; gov-; poten-; regi-; tyran-.