"revolving stone disc used for sharpening, etc." is from c. 1400. Phrase nose to the grindstone in use by 1530s; originally to get control of another and treat him harshly:
This Text holdeth their noses so hard to the grindstone, that it clean disfigureth their Faces. [John Frith, "Mirror to know Thyself," 1532]
The phrase's main modern (reflexive) sense of "working hard" is from 1828.
1570s, "perceive the smell of;" 1640s; "pry, search in a meddlesome way;" from nose (n.). Related: Nosed; nosing.
Middle English kēpen, from late Old English cepan (past tense cepte) "to seize, hold; seek after, desire," also "to observe or carry out in practice; look out for, regard, pay attention to," from Proto-Germanic *kopjan, which is of uncertain origin. Old English cepan was used c. 1000 to render Latin observare, so perhaps it is related to Old English capian "to look" (from Proto-Germanic *kap-), which would make the basic sense "to keep an eye on, see to it."
The word prob. belonged primarily to the vulgar and non-literary stratum of the language; but it comes up suddenly into literary use c. 1000, and that in many senses, indicating considerable previous development. [OED]
The senses exploded in Middle English: "to guard, defend" (12c.); "restrain (someone) from doing something" (early 13c.); "take care of, look after; protect or preserve (someone or something) from harm, damage, etc." (mid-13c.); "preserve, maintain, carry on" a shop, store, etc. (mid-14c.); "prevent from entering or leaving, force to remain or stay" (late 14c.); "preserve (something) without loss or change," also "not divulge" a secret, private information, etc., also "to last without spoiling" (late 14c.); "continue on" (a course, road, etc.), "adhere to" a course of action (late 14c.); "stay or remain" (early 15c.); "to continue" (doing something) (mid-15c.). It is used to translate both Latin conservare "preserve, keep safe" and tenere "to keep, retain."
From 1540s as "maintain for ready use;" 1706 as "have habitually in stock for sale." Meaning "financially support and privately control" (usually in reference to mistresses) is from 1540s; meaning "maintain in proper order" (of books, accounts) is from 1550s.
To keep at "work persistently" is from 1825; to keep on "continue, persist" is from 1580s. To keep up is from 1630s as "continue alongside, proceed in pace with," 1660s as "maintain in good order or condition, retain, preserve," 1680s as "support, hold in an existing state." To keep it up "continue (something) vigorously" is from 1752. To keep to "restrict (oneself) to" is from 1711. To keep off (trans.) "hinder from approach or attack" is from 1540s; to keep out (trans.) "prevent from entering" is from early 15c.
Middle English nose, from Old English nosu "the nose of the human head, the special organ of breathing and smelling," from Proto-Germanic *nuso- (source also of Old Norse nös, Old Frisian nose, Dutch neus, Old High German nasa, German Nase), from PIE root *nas- "nose."
Used of beaks or snouts of animals from mid-13c.; of any prominent or projecting part supposed to resemble a nose from late 14c. (nose cone in the space rocket sense is from 1949). Meaning "sense of smell" is from mid-14c. Meaning "odor, scent" is from 1894. In Middle English, to have one's spirit in one's nose was to "be impetuous or easily angered" (c. 1400).
Kiv, It could bee no other then his owne manne, that had thrust his nose so farre out of ioynte. ["Barnabe Riche His Farewell to Military Profession," 1581]
To pay through the nose "pay excessively" (1670s) seems to suggest bleeding. Many extended meanings are from the horse-racing sense of "length of a horse's nose," as a measure of distance between two finishers (1908). To turn up one's nose "show disdain, express scorn or contempt" is from 1818 (earlier hold up one's nose, 1570s); a similar notion is expressed in look down one's nose (1907). To say something is under (one's) nose "in plain view, directly in front of one" is from mid-15c. To be as plain as the nose on one's face "very easy to be seen or understood" is from 1590s.
"a nose turned upwards at the tip," 1778, from pug (n.) based on fancied similarity to the nose of either the monkey or the dog. Related: Pug-nosed (1791). Pug-face is attested by 1768.