"motherless calf in a herd," 1887, cowboy slang, of uncertain origin. It may have had an earlier, more specific meaning:

What is called a "dogie" is a scrub Texas yearling. Dogies are the tailings of a mixed herd of cattle which have failed of a ready sale while on the market. They are picked up finally by purchasers in search of cheap cattle; but investments in such stock are risky and have proven to be disastrous this winter. [The Breeder's Gazette, March 5, 1885]

"young cow that has not had a calf," Middle English heifer, from Old English heahfore (West Saxon); Northumbrian hehfaro, heffera (plural), "heifer," of unknown origin, not found outside English.

The first element seems to be heah "high," which is common in Old English compounds with a sense of "great in size." The second element might be from a fem. form of Old English fearr "bull," from Proto-Germanic *farzi-, from PIE root *pere- (1) "to produce, bring forth." Or it might be related to Old English faran "to go" (giving the whole a sense of "high-stepper"); but there are serious sense difficulties with both conjectures. Liberman offers this alternative:

Old English seems to have had the word *hægfore 'heifer.' The first element (*hæg-) presumably meant 'enclosure' (as do haw and hedge), whereas -fore was a suffix meaning 'dweller, occupant' ....

In modern use, a female that has not yet calved, as opposed to a cow (n.), which has, and a calf (n.1), which is an animal of either sex not more than a year old. As derisive slang for "a woman, girl" it dates from 1835. 

"salted and peppered raw egg, drunk in booze or vinegar," by 1878, American English, from prairie + oyster (in reference to the taste or the method of consuming it). Also called prairie-cocktail (1889). Prairie-oyster as "fried calf testicle," considered a delicacy, is by 1941.

PRAIRIE OYSTER. This simple but very nutritious drink may be taken by any person of the most delicate digestion, and has become one of the most popular delicacies since its introduction by me at Messrs. Spiers and Pond's. Its mode of preparation is very simple. Into a wine glass pat a new-laid egg ; add half a tea-spoonful of vinegar, dropping it gently down on the inside of the glass ; then drop on the yolk a little common salt, sufficient not to quite cover half the size of a threepenny-piece; pepper according to taste, The way to take this should be by placing the glass with the vinegar furthest from the mouth and swallow the contents. The vinegar being the last gives it more of an oyster-like flavour. [Leo Engel, "American & Other Drinks," London, 1878]

"contractible animal tissue consisting of bundles of fibers," late 14c., "a muscle of the body," from Latin musculus "a muscle," literally "a little mouse," diminutive of mus "mouse" (see mouse (n.)).

So called because the shape and movement of some muscles (notably biceps) were thought to resemble mice. The analogy was made in Greek, too, where mys is both "mouse" and "muscle," and its combining form gives the medical prefix myo-. Compare also Old Church Slavonic mysi "mouse," mysica "arm;" German Maus "mouse; muscle," Arabic 'adalah "muscle," 'adal "field mouse;" Cornish logodenfer "calf of the leg," literally "mouse of the leg." In Middle English, lacerte, from the Latin word for "lizard," also was used as a word for a muscle.

Musclez & lacertez bene one selfe þing, Bot þe muscle is said to þe fourme of mouse & lacert to þe fourme of a lizard. [Guy de Chauliac, "Grande Chirurgie," c. 1425]

Hence muscular and mousy are relatives, and a Middle English word for "muscular" was lacertous, "lizardy." Figurative sense of "muscle, strength, brawn" is by 1850; that of "force, violence, threat of violence" is 1930, American English. Muscle car "hot rod" is from 1969.

"large carnivorous or omnivorous mammal of the family Ursidae," Old English bera "a bear," from Proto-Germanic *bero, literally "the brown (one)" (source also of Old Norse björn, Middle Dutch bere, Dutch beer, Old High German bero, German Bär), usually said to be from PIE root *bher- (2) "bright; brown." There was perhaps a PIE *bheros "dark animal" (compare beaver (n.1) and Greek phrynos "toad," literally "the brown animal").

Greek arktos and Latin ursus retain the PIE root word for "bear" (*rtko; see arctic), but it is believed to have been ritually replaced in the northern branches because of hunters' taboo on names of wild animals (compare the Irish equivalent "the good calf," Welsh "honey-pig," Lithuanian "the licker," Russian medved "honey-eater"). Others connect the Germanic word with Latin ferus "wild," as if it meant "the wild animal (par excellence) of the northern woods."

Symbolic of Russia since 1794. Used of rude, gruff, uncouth men since 1570s. Stock market meaning "speculator for a fall" is 1709 shortening of bearskin jobber (from the proverb sell the bearskin before one has caught the bear); i.e. "one who sells stock for future delivery, expecting that meanwhile prices will fall." Paired with bull from c. 1720. Bear claw as a type of large pastry is from 1942, originally chiefly western U.S. Bear-garden (1590s) was a place where bears were kept for the amusement of spectators.

late 13c., from a Scandinavian source, probably Old Norse leggr "a leg, bone of the arm or leg," from Proto-Germanic *lagjaz (cognates Danish læg, Swedish läg "the calf of the leg"), a word with no certain ulterior connections. Perhaps from a PIE root meaning "to bend" [Buck]. For Old Norse senses, compare Bein, the German word for "leg," in Old High German "bone, leg" (see bone (n.)). Replaced Old English shank (n.), itself also perhaps from a root meaning "crooked."

Distinguished from an arm, leg, or fin in being used for support. Of triangle sides from 1650s (translating Greek skelos, literally "leg"). Extended to furniture supports from 1670s. Meaning "part of pants which cover the leg" is from 1570s. By 1870s as an adjective it had a salacious suggestion of artistic displays focused on the female form, such as leg-piece in theater jargon, leg-business as slang for "ballet."

The meaning "a part or stage of a journey or race" (1920) is from earlier sailing sense of "a run made by a ship on a single tack when beating to windward" (1867), which was usually qualified as long leg, short leg, etc. Slang phrase shake a leg is attested from 1869 as "dance," 1880 as "hurry up." To be on (one's) last legs "at the end of one's life" is from 1590s, the notion is of something that serves one for support and keeps one moving. To take leg bail was old slang for "run away" (1774). Legs "ability to be an enduring success, staying power" is from 1970s show business slang.

1867, "calf or yearling found without an owner's brand," a word from the great cattle ranches of the American West, so called for Samuel A. Maverick (1803-1870), Texas cattle owner who was notoriously negligent in branding his calves.

All neat stock found running at large in this State, without a mother, and upon which there is neither mark nor brand, shall be deemed a maverick, and shall be sold to the highest bidder for cash, at such time and place, and under such rules and regulations, as the round-up commissioners of the district shall prescribe. [act to amend the General Statutes of the State of Colorado, approved April 8, 1885]

The family name is an old one in Boston, and a different Samuel Maverick was killed in the Boston Massacre. The sense of "individualist, unconventional person" is said to be attested by 1886, via the notion of "masterless," but its modern popularity  seems to date to the late 1930s and the career of Maury Maverick (1895-1954) of Texas, grandson of Samuel the rancher and a Democratic congressman 1935-1939 famous for his liberal independent streak, who also coined gobbledygook.

"The Crisis" (April 1939) wrote that "During his stormy career in Washington Maverick became known as the one dependable liberal among the southerners. He recognized the broad problems of our nation, refusing to allow his vision to be limited by sectional prejudices, or racial or economic bugaboos. He was the only southern congressman to vote for the Gavagan federal anti-lynching bill. Not only did he vote for it, but he made a speech on the floor of the House in support of it."