"fine, minute, loose, uncompacted particles," c. 1300, poudre, "ash, cinders; dust of the earth;" early 14c. of any pulverized substance; from Old French poudre "dust, powder; ashes; powdered substance" (13c.), earlier pouldre (11c.), from Latin pulverem (nominative pulvis) "dust, powder" (source also of Spanish polvo, Italian polve; see pulverize).
The insertion of the unetymological -d- was common in French (compare meddle, tender (adj.), remainder). German has it as a doublet; Puder via French and Pulver from Latin. From mid-14c. specifically as "medicinal powder;" specialized sense of "gunpowder" is from late 14c. In the sense "powdered cosmetic," it is recorded from 1570s.
Powder keg "small barrel for holding gunpowder" is by 1820; the figurative sense ("something likely to explode easily") is by 1895. Powder room, euphemistic for "women's lavatory," is attested from 1936. Earlier it meant "place where gunpowder is stored on a warship" (1620s). Powder monkey "boy employed on ships to carry powder from the magazines to the guns" is from 1680s. Powder blue (1650s) was smalt used in laundering; as a color name from 1894.
The phrase take a powder "scram, vanish," is from 1920; it was a common phrase as a doctor's instruction, so perhaps the notion is of taking a laxative medicine or a sleeping powder, with the result that one has to leave in a hurry (or, on another guess, from a magician's magical powder, which makes things disappear).
Avis dropped an exhausted little heap onto her aunt's bed. She put her hand over her heart and said piteously, "Oh, Aunt Joyce, I mustn't ever do that again. My heart's going awful fast. I shall have to take a powder. Wasn't it fun though-" Avis' dark eyes flashed. [from "The Evolution of Avis" in The Connecticut School Journal, Jan. 9, 1902]
When the wife of your breast has confessed she has drest
On just triple the sum you allowed her,
And has run up long bills for her frocks and her frills—
Take a powder, my friend, take a powder.
[from "The Panacaea," in Punch, Dec. 14, 1901]
Powder in the wind (c. 1300, meaning powdered spices) was a Middle English image of something highly valued but flawed in some way that renders it impermanent or doomed to loss (of virtues without humility, etc.).
c. 1300, poudren, "to put or sprinkle powder on;" late 14c., "to make into powder," from Old French poudrer "to pound, crush to powder; strew, scatter," from poudre (see powder (n.)). Specifically as "to whiten cosmetically by some application of white material in powder form" is from 1590s. Related: Powdered; powdering.
Old English horn "horn of an animal; projection, pinnacle," also "wind instrument" (originally one made from animal horns), from Proto-Germanic *hurni- (source also of German Horn, Dutch horen, Old Frisian horn, Gothic haurn), from PIE root *ker- (1) "horn; head."
Late 14c. as "one of the tips of the crescent moon." The name was retained for a class of musical instruments that developed from the hunting horn; the French horn is the true representative of the class. Of dilemmas from 1540s; of automobile warning signals from 1901. Slang meaning "erect penis" is suggested by c. 1600. Jazz slang sense of "trumpet" is by 1921. Meaning "telephone" is by 1945. Figurative senses of Latin cornu included "salient point, chief argument; wing, flank; power, courage, strength." Horn of plenty is from 1580s. To make horns at "hold up the fist with the two exterior fingers extended" as a gesture of insult is from c.1600.
Symbolic of cuckoldry since mid-15c. (the victim was fancied to grow one on his head). The image is widespread in Europe and perhaps as old as ancient Greece. The German linguist Hermann Dunger ('Hörner Aufsetzen' und 'Hahnrei', "Germania" 29, 1884) ascribes it to a custom surviving into 19c., "the old practice of engrafting the spurs of a castrated cock on the root of the excised comb, which caused them to grow like horns" [James Hastings, "Encyclopedia of Religion and Ethics"] but the image could have grown as well from a general gesture of contempt or insult made to wronged husbands, "who have been the subject of popular jest in all ages" [Hastings].
word-forming element meaning "horn, horn-like part," from Latinized form of Greek keras (genitive keratos) "horn of an animal; horn as a substance," from PIE root *ker- (1) "horn, head."