early 15c., dejecten, "to throw or cast down," a sense now obsolete, from Latin deiectus "a throwing down, felling, fall," past participle of deicere "to cast down, destroy; drive out; kill, slay, defeat," from de- "down" (see de-) + -icere, combining form of iacere "to throw" (from PIE root *ye- "to throw, impel"). The figurative sense of "depress in spirit, discourage, dispirit" is from c. 1500.
"to cause to be or appear lower or more humble; depress, especially to abase in estimation; subject to shame or disgrace; mortify," 1530s, a back-formation from humiliation or else from Late Latin humiliatus, past participle of humiliare "to humble," from humilis "lowly, humble," literally "on the ground," from humus "earth" (from PIE root *dhghem- "earth"). Earlier was humily "humble oneself" (mid-15c.), from Old French humilier. Related: Humiliated.
late 14c., "reduce in rank, etc.," from Old French abaissier "diminish, make lower in value or status; lower oneself" (12c.), literally "bend, lean down," from Vulgar Latin *ad bassiare "bring lower," from ad "to, toward" (see ad-) + Late Latin bassus "low, short" (see base (adj.)).
The form in English was altered 16c. by influence of base (adj.), making the word an exception to the rule that Old French verbs with stem -iss- enter English as -ish (comprehension might have played a role; earlier forms of abase often are identical with those of abash). Literal sense of "lower, depress" (late 15c.) is archaic or obsolete. Related: Abased; abasing.
"cause a drop in the pressure of a gas in a certain space," 1944; see de- + pressurize. Related: Depressurized; depressurizing; depressurization.
c. 1300, "knob or ball attached to another body," especially as used to hold together different parts of a garment by being passed through a slit or loop (surname Botouner "button-maker" attested from mid-13c.), from Old French boton "a button," originally "a bud" (12c., Modern French bouton), from bouter, boter "to thrust, strike, push," common Romanic (cognate with Spanish boton, Italian bottone), ultimately from a Germanic source, from Proto-Germanic *buttan, from PIE root *bhau- "to strike." Thus a button is, etymologically, something that pushes up, or thrusts out.
The meaning "point of the chin" is pugilistic slang, by 1921. A button as a round protuberance you depress to create an effect by closing an (electrical) circuit is attested from 1840s. Button-pusher as "deliberately annoying or provocative person" is attested by 1990 (in reference to Bill Gates, in "InfoWorld" magazine, Nov. 19). In the 1980s it meant "photographer."
c. 1400, "unlucky, inauspicious," in dismal day, earlier as a noun, in the dismal (c. 1300) "in days of misfortune or disaster, under inauspicious circumstances, at an unlucky time," from Anglo-French dismal (mid-13c.), apparently from Old French (li) dis mals "(the) bad days," from Medieval Latin dies mali "evil or unlucky days" (also called dies Ægyptiaci), from Latin dies "days" (from PIE root *dyeu- "to shine") + mali, plural of malus "bad" (from PIE root *mel- (3) "false, bad, wrong").
Through the Middle Ages, calendars marked as unlucky two days of each month (Jan. 1, 25; Feb. 4, 26; March 1, 28; April 10, 20; May 3, 25; June 10, 16; July 13, 22; Aug. 1, 30; Sept. 3, 21; Oct. 3, 22; Nov. 5, 28; Dec. 7, 22), supposedly based on the ancient calculations of Egyptian astrologers.
By 1580s the English word had been extended to "gloomy, dreary, cheerless," and was used to describe physical surroundings, sounds, or anything else felt as tending to depress the spirits. In North America, it was the name given along the seacoast and sounds around North Carolina to tracts of swampy land and dead trees (1763). The dismal science (1849) was Carlyle's name for "political economics." Related: Dismally.