Etymology
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ace (n.)

c. 1300, "one at dice," from Old French as "one at dice" (12c.), from Latin as "a unit, one, a whole, unity;" also the name of a small Roman coin (originally a rectangular bronze plaque weighing one pound, it eventually was reduced by depreciation to half an ounce; in imperial times it became a round coin). The Latin word also is the source of Spanish as, Italian asso, German ass, Dutch aas, Danish es. It is perhaps originally Etruscan and related to Greek heis "one" (from PIE root *sem- (1) "one, as one"), or it might be taken directly into Latin from the Greek word.

In English, it meant the side of the die with only one mark before it meant the playing card with one pip (1530s). Because this was the lowest roll at dice, ace was used metaphorically in Middle English for "bad luck" or "something of no value;" but as the ace often is the highest playing card, the extended senses based on "excellence, good quality" arose 18c. as card-playing became popular. Ace in the hole in the figurative sense of "concealed advantage" is attested from 1904, from crooked stud poker deals.

Meaning "outstanding pilot" dates from 1917 (technically, in World War I aviators' jargon, one who has brought down 10 enemy planes, though originally in reference to 5 shot down), from French l'ace (1915), which, according to Bruce Robertson (ed.) "Air Aces of the 1914-1918 War" was used in prewar French sporting publications for "top of the deck" boxers, cyclists, etc. Sports meaning "point scored" (1819) led to sense of "unreturnable serve" (by 1889).

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ace (v.)

"to score" in sports, 1922, in tennis, from ace (n.). This probably is the source of the student slang sense of "get high marks" (1959). Related: Aced; acing.

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Deely-bobber (n.)

"headband with two springs carrying ornaments," 1982, trademark name held by Ace Novelty Company. Earlier it had been a patent name for a type of building blocks, manufactured 1969-1973.

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spade (n.2)

black figure on playing cards," 1590s, probably from Italian spade, plural of spada "the ace of spades," literally "sword, spade," from Latin spatha "broad, flat weapon or tool," from Greek spathe "broad blade" (see spade (n.1)). Phrase in spades "in abundance" first recorded 1929 (Damon Runyon), probably from bridge, where spades are the highest-ranking suit.

The invitations to the musicale came sliding in by pairs and threes and spade flushes. [O.Henry, "Cabbages & Kings," 1904]

Derogatory meaning "black person" is 1928, from the color of the playing card symbol.

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*oi-no- 
Proto-Indo-European root meaning "one, unique."

It forms all or part of: a (1) indefinite article; alone; an; Angus; anon; atone; any; eleven; inch (n.1) "linear measure, one-twelfth of a foot;" lone; lonely; non-; none; null; once; one; ounce (n.1) unit of weight; quincunx; triune; unanimous; unary; une; uni-; Uniate; unilateral; uncial; unicorn; union; unique; unison; unite; unity; universal; universe; university; zollverein.

It is the hypothetical source of/evidence for its existence is provided by: Greek oinos "ace (on dice);" Latin unus "one;" Old Persian aivam; Old Church Slavonic -inu, ino-; Lithuanian vienas; Old Irish oin; Breton un "one;" Old English an, German ein, Gothic ains "one."
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quark (n.)

hypothetical subatomic particle having a fractional electric charge, 1964, applied by U.S. physicist Murray Gell-Mann (1929-2019), who said in correspondence with the editors of the OED in 1978 that he took it from a word in James Joyce's "Finnegans Wake" (1939), but also that the sound of the word was in his head before he encountered the printed form in Joyce.

German Quark "curds, rubbish" has been proposed as the ultimate inspiration [Barnhart; Gell-Mann's parents were immigrants from Austria-Hungary]; it is from Old Church Slavonic tvarogu "curds, cottage cheese" (from a suffixed form of PIE root *teue- "to swell," source also of Greek tyros "cheese"). George Zweig, Gell-Mann's co-proposer of the theory, is said to have preferred the name ace for them.

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acetate (n.)

by 1790 in a translation of Fourcroy, "salt formed by combining acetic acid with a base," from Latin acetum "vinegar" (see acetic) + chemical suffix -ate (3). As a type of synthetic material, it is attested from 1920, short for acetate silk (1912), etc.

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acetylene (n.)

gaseous hydrocarbon, 1860, from French acétylène, coined by French chemist Pierre Eugène Marcellin Berthelot from chemical ending -ene + acetyl, which was coined from acetic + -yl in 1839 by German chemist Justus von Liebig. Liebig's coinage was in reference to a different radical; acetyl was transferred to its current sense in 1850s, but Berthelot's coinage was based on the original use of acetyl.

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-aceous 
word-forming element denoting "belonging to, of the nature of," from Latin -aceus, enlarged form of adjectival suffix -ax (genitive -acis); see -acea. Especially in biology, "pertaining to X order of plants or animals."
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acervulus (n.)

"brain-sand" (anatomical), 1806, medical Latin, literally "little heap," diminutive of Latin acervus "heap," which is akin to acer "sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce").

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