master-work n.

late Old English mægester "a man having control or authority over a place; a teacher or tutor of children," from Latin magister (n.) "chief, head, director, teacher" (source of Old French maistre, French maître, Spanish and Italian maestro, Portuguese mestre, Dutch meester, German Meister), contrastive adjective ("he who is greater") from magis (adv.) "more," from PIE *mag-yos-, comparative of root *meg- "great." The form was influenced in Middle English by Old French cognate maistre.

From late 12c. as "man eminently or perfectly skilled in something," also "one who is chief teacher of another (in religion, philosophy, etc.), religious instructor, spiritual guide." Sense of "master workman or craftsman, workman who is qualified to teach apprentices and carry on a trade on his own account" is from c. 1300. The meaning "one charged with the care, direction, oversight, and control of some office, business, etc." is from mid-13c.; specifically as "official custodian of certain animals kept for sport" early 15c. (maister of þe herte houndes; the phrase master of the hounds is attested by 1708). As a title of the head or presiding officer of an institution, late 14c.; as "captain of a merchant vessel" early 14c.

In the broadest sense, "one who has power to control, use, or dispose (of something or some quality) at will," from mid-14c. Also from mid-14c. as "one who employs another or others in his service" (in which sense the correlative word was servant, man, or apprentice); also "owner of a living creature" (a dog, a horse, also, in ancient contexts a slave); paired with slave in the legal language of the American colonies by 1705 in Virginia.

In academic sense "one who has received a specific degree" (translating Medieval Latin magister) it is attested from mid-13c., originally "one who has received a degree conveying authority to teach in the universities;" master's degree, originally a degree giving one authority to teach in a university, is from late 14c.

Also used in Middle English of dominant women. From 1530s as "male head of a household." As a title or term of respect or rank, mid-14c. As a title prefixed to the name of a young gentleman or boy of the better not old enough to be called Mr., short for young master (late 16c.). Sense of "chess player of the highest at national or international level" is by 1894. Meaning "original of a recording" is by 1904.

As an adjective from late 12c. Master-key, one that will open ("master") a number of locks so differently constructed that the key proper to each will open none of the others" is from 1570s. Master race "race of people considered to be pre-eminent in greatness or power" (typical in reference to Nazi theories of the Aryan race, perhaps based on German Herrenvolk) is by 1935. From 1530 as "artist of distinguished skill;" old masters is attested by 1733.

Master bedroom, "bedroom designed for the use of the owner of the property," as opposed to bedrooms for children or guests, is by 1919 in U.S. home-builders publications (e.g. Building Age, April 1919).  It seems to be based on the English master's bedroom (by 1903) "bedroom of a headmaster or other master at an English boarding school or other similar institution."

The top floor was treated much the same as the two lower ones. Here the closet was made just a bit larger so as to allow for a bathtub, thus pushing the partition forward, making the front room less deep than the rooms below, yet paradoxically larger, because it takes in the whole front of the house. This is what is known in English advertisements as the "Master's bedroom." [The House Beautiful, June 1921] 

Old English weorc, worc "something done, discrete act performed by someone, action (whether voluntary or required), proceeding, business; that which is made or manufactured, products of labor," also "physical labor, toil; skilled trade, craft, or occupation; opportunity of expending labor in some useful or remunerative way;" also "military fortification." This is from Proto-Germanic *werka- "work" (source also of Old Saxon, Old Frisian, Dutch werk, Old Norse verk, Middle Dutch warc, Old High German werah, German Werk, Gothic gawaurki), from PIE *werg-o-, a suffixed form of the root *werg- "to do."

The meaning "physical effort, exertion" is from c. 1200; that of "scholarly labor" or its productions is from c. 1200; the meaning "artistic labor" or its productions is from c. 1200. The sense of "labor as a measurable commodity" is from c. 1300. The meaning "embroidery, stitchery, needlepoint" is from late 14c.

Work of art attested by 1774 as "artistic creation," earlier (1728) "artifice, production of humans (as opposed to nature)." Work ethic recorded from 1959. To be out of work "unemployed" is from 1590s. To make clean work of is from c. 1300; to make short work of is from 1640s.

Proverbial expression many hands make light work is from c. 1300. To have (one's) work cut out for one is from 1610s; to have it prepared and prescribed, hence, to have all one can handle. Work in progress is from 1930 in a general sense, earlier as a specific term in accountancy and parliamentary procedure.

Work is less boring than amusing oneself. [Baudelaire, "Mon Coeur mis a nu," 1862]