master

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that has control over another person, a group of persons, or a thing, especially.
• noun The owner or keeper of an animal.
• noun The owner of a slave.
• noun One who has control over or ownership of something.
• noun An employer.
• noun The man who serves as the head of a household.
• noun One who defeats another; a victor.
• noun A man who acts out the role of the dominating partner in a sadomasochistic relationship.
• noun The captain of a merchant ship.
• noun One whose teachings or doctrines are accepted by followers.
• noun Christianity Jesus.
• noun A male teacher, schoolmaster, or tutor.
• noun One who holds a master's degree.
• noun An artist or performer of great and exemplary skill.
• noun An old master.
• noun A worker qualified to teach apprentices and carry on the craft independently.
• noun An expert.
• noun Used formerly as a title for a man holding a naval office ranking next below a lieutenant on a warship.
• noun Used as a title for a man who serves as the head or presiding officer of certain societies, clubs, orders, or institutions.
• noun Used as a title for any of various male officers having specified duties concerning the management of the British royal household.
• noun Used as a courtesy title before the given or full name of a boy not considered old enough to be addressed as Mister.
• noun Archaic Used as a form of address for a man; mister.
• noun One who is appointed to assist a court in the performance of certain legal functions, such as the taking of testimony and calculating damages in complex litigation.
• noun A man who owns a pack of hounds or is the chief officer of a hunt.
• noun An original, such as an original document or audio recording, from which copies can be made.
• adjective Of, relating to, or characteristic of a master.
• adjective Principal or predominant.
• adjective Controlling all other parts of a mechanism.
• adjective Highly skilled or proficient.
• adjective Being an original from which copies are made.
• transitive verb To become very skilled in or knowledgeable about.
• transitive verb To overcome or defeat.
• transitive verb To produce a master copy of (an audio or video recording, for example).

from The Century Dictionary.

• To become the master of; subject to one's will, control, or authority; conquer; overpower; subdue.
• To make one's self master of; overcome the difficulties of; learn so as to be able to apply or use: as, to master a science.
• To control as master or owner; possess; have power over.
• To hold the position or relation of master to; be a master to.
• In a technical use, to season or age.
• To be skilful; excel.
• noun A vessel with (a specified number of) masts: in composition: as, a three-master.
• noun A man who has authority; a man who exercises the chief control over something or some one; a paramount ruler, governor, or director.
• noun Specifically - A male teacher or instructor in a school, more especially the sole or head teacher; a schoolmaster.
• noun The navigator of a ship. In the merchant marine the master is the captain or commander. In men-of-war the navigator or sailing-master formerly had the specific title of master, and was a line-officer of the lowest rank. In the British navy his title is now navigating-lieutenant or staff-commander. In the United States navy he is now ranked as lieutenant (junior grade), between eusign and lieutenant, and is called the navigator.
• noun One who has another or others under his immediate control; a lord paramount or employer of slaves, vassals, domestic servants, workmen, or laborers, etc.; in law, specifically, one who has in his own right and by virtue of contract a legal personal authority over the services of another, such other being called his servant.
• noun One charged with the care, direction, oversight, or control of some office, business, undertaking, or department: as, Master of the Rolls; a ship-, harbor-, or dock-master; master of the revels, ceremonies, etc.
• noun One who has the power of controlling or using at pleasure; an owner or proprietor; a disposer.