palfrey (n.)

Middle English riden, from Old English ridan "sit or be carried on" (as on horseback), "move forward; rock; float, sail" (class I strong verb; past tense rad, past participle riden), from Proto-Germanic *ridan (source also of Old Norse riða, Old Saxon ridan, Old Frisian rida "to ride," Middle Dutch riden, Dutch rijden, Old High German ritan, German reiten), from PIE *reidh- "to ride" (source also of Old Irish riadaim "I travel," Old Gaulish reda "chariot"). Common to Celtic and Germanic, perhaps a loan word from one to the other.

Of a ship, "to sail, float, rock," c. 1300. The meaning "heckle" is by 1912 from earlier sense of "dominate cruelly, have the mastery of, harass at will" (1580s) on the notion of "control and manage," as a rider does a horse, especially harshly or arrogantly. The verb in venery is from mid-13c.

To ride out "endure (a storm, etc.) without great damage" is from 1520s, literal and figurative. To let (something) ride "allow to pass without comment or intervention" is by 1921. To ride herd on "guard and control" is by 1897, from cattle-driving. To ride shotgun "ride in the passenger seat of an automobile" is by 1919, from the custom of having an armed man up beside the driver of a stagecoach to ward off trouble. To ride shank's mare "walk" is from 1846 (see shank (n.)). The ____ rides again cliche is from Hollywood movie titles ("Destry Rides Again," 1939).

"solidungulate perissodactyl mammal of the family Equidæ and genus Equus" [Century Dictionary], Old English hors "horse," from Proto-Germanic *harss- (source also of Old Norse hross, Old Frisian, Old Saxon hors, Middle Dutch ors, Dutch ros, Old High German hros, German Roß "horse"), of unknown origin. By some, connected to PIE root *kers- "to run," source of Latin currere "to run." Boutkan prefers the theory that it is a loan-word from an Iranian language (Sarmatian) also borrowed into Uralic (compare Finnish varsa "foal"),

The usual Indo-European word is represented by Old English eoh, Greek hippos, Latin equus, from PIE root *ekwo-. Another Germanic "horse" word is Old English vicg, from Proto-Germanic *wegja- (source also of Old Frisian wegk-, Old Saxon wigg, Old Norse vigg), which is of uncertain origin. In many other languages, as in English, this root has been lost in favor of synonyms, probably via superstitious taboo on uttering the name of an animal so important in Indo-European religion. For the Romanic words (French cheval, Spanish caballo) see cavalier (n.); for Dutch paard, German Pferd, see palfrey; for Swedish häst, Danish hest see henchman. As plural Old English had collective singular horse as well as horses, in Middle English also sometimes horsen, but horses has been the usual plural since 17c.

Used at least since late 14c. of various devices or appliances which suggest a horse (as in sawhorse), typically in reference to being "that upon which something is mounted." For sense of "large, coarse," see horseradish. Slang use for "heroin" is attested by 1950.

To ride a horse that was foaled of an acorn (1670s) was through early 19c. a way to say "be hanged from the gallows." Horse latitudes is attested by 1777, the name of unknown origin despite much speculation. A horse-pistol (by 1704) was a large one-handed pistol used by horseback riders. A dead horse as a figure for something that has ceased to be useful is from 1630s; to flog a dead horse "attempt to revive interest in a worn-out topic" is from 1864.

HORSEGODMOTHER, a large masculine wench; one whom it is difficult to rank among the purest and gentlest portion of the community. [John Trotter Brockett, "A Glossary of North Country Words," 1829]

The term itself is attested from 1560s. The horse's mouth as a source of reliable information is from 1921, perhaps originally of racetrack tips, from the fact that a horse's age can be determined by looking at the teeth (compare gift horse under gift (n.)).

To swap horses while crossing the river (a bad idea) is from the American Civil War and appears to have been originally one of Abe Lincoln's stories.

Horse-and-buggy meaning "old-fashioned" is recorded from 1926 slang, originally in reference to a "young lady out of date, with long hair." To hold (one's) horses "restrain one's enthusiasm, be patient" is from 1842, American English; the notion is of keeping a tight grip on the reins.