1590s, "being," from Late Latin entitatem (nominative entitas), from ens (genitive entis) "a thing," proposed by Caesar as present participle of esse "be" (see is), to render Greek philosophical term to on "that which is" (from neuter of present participle of einai "to be," from PIE root *es- "to be"). Originally abstract; concrete sense in English is from 1620s.
early 14c., quantite, "amount, magnitude, the being so much in measure or extent," from Old French quantite, cantite (12c., Modern French quantité) and directly from Latin quantitatem (nominative quantitas) "relative greatness or extent," coined as a loan-translation of Greek posotes (from posos "how great? how much?") from Latin quantus "of what size? how much? how great? what amount?," correlative pronominal adjective (from PIE root *kwo-, stem of relative and interrogative pronouns).
From late 14c. as "that which has quantity, a concrete quantity;" from 1610s in the concrete sense of "an object regarded as more or less." In prosody and metrics, "the relative time occupied in uttering a vowel or syllable" (distinguishing it as long or short) by 1560s. Latin quantitatem also is the source of Italian quantita, Spanish cantidad, Danish and Swedish kvantitet, German quantitat.
1784, "descent of a Hindu deity to earth in an incarnate or tangible form," from Sanskrit avatarana "descent" (of a deity to the earth in incarnate form), from ava- "off, down" (from PIE root *au- (2) "off, away") + base of tarati "(he) crosses over," from PIE root *tere- (2) "cross over, pass through, overcome."
Meaning "concrete embodiment of something abstract" is from 1815. In computer use, it seems to trace to the novel "Snowcrash" (1992) by Neal Stephenson.
1757, "situated between two things;" 1818 as "serving as a mediator;" from French intermédiaire (17c.), from Latin intermedius "that which is between" (see intermediate). As a noun, "one who acts between others" from 1791 (Medieval Latin intermedium also was used as a noun). An earlier adjective was intermedial (1590s).
Intermediary, n., is, even with concrete sense of go-between or middleman or mediator, a word that should be viewed with suspicion & resorted to only when it is clear that every more ordinary word comes short of the need. [Fowler]
Two long-time Pentagon stand-bys are fly-speckers and nit-pickers. The first of these nouns refers to people whose sole occupation seems to be studying papers in the hope of finding flaws in the writing, rather than making any effort to improve the thought or meaning; nit-pickers are those who quarrel with trivialities of expression and meaning, but who usually end up without making concrete or justified suggestions for improvement. [Collier's, Nov. 24, 1951]
late 14c., nocioun, "a general concept, conception," from Latin notionem (nominative notio) "concept, conception, idea, notice," noun of action from past participle stem of noscere "come to know," from PIE root *gno- "to know." Coined by Cicero as a loan-translation of Greek ennoia "act of thinking, notion, conception," or prolepsis "previous notion, previous conception."
Meaning "an opinion, a view, a somewhat vague belief" is from c. 1600; that of "a not very rational inclination, a whim" is by 1746. Notions in the concrete sense of "miscellaneous small articles of convenience or utensils" (such as sold by Yankee peddlers) is by 1803, American English, via the idea of "clever product of invention."
late 14c., originally in grammar (in reference to certain nouns that do not name concrete things), from Latin abstractus "drawn away," past participle of abstrahere "to drag away, detach, pull away, divert;" also figuratively, from assimilated form of ab "off, away from" (see ab-) + trahere "to draw," from PIE root *tragh- "to draw, drag, move" (see tract (n.1)).
The meaning in philosophy, "withdrawn or separated from material objects or practical matters" (opposed to concrete) is from mid-15c. That of "difficult to understand, abstruse" is from c. 1400.
In the fine arts, "characterized by lack of representational qualities" by 1914; it had been a term in music at least since 1847 for music without accompanying lyrics. Abstract expressionism as an American-based uninhibited approach to art exemplified by Jackson Pollock is from 1952, but the term itself had been used in the 1920s of Kandinsky and others.
Oswald Herzog, in an article on "Der Abstrakte Expressionismus" (Sturm, heft 50, 1919) gives us a statement which with equal felicity may be applied to the artistic attitude of the Dadaists. "Abstract Expressionism is perfect Expressionism," he writes. "It is pure creation. It casts spiritual processes into a corporeal mould. It does not borrow objects from the real world; it creates its own objects .... The abstract reveals the will of the artist; it becomes expression. ..." [William A. Drake, "The Life and Deeds of Dada," 1922]
Then, that art we have called "abstract" for want of any possible descriptive term, with which we have been patient, and, even, appreciative, getting high stimulation by the new Guggenheim "non-objective" Art Museum, is reflected in our examples of "surrealism," "dadaism," and what-not, to assert our acquaintance in every art, fine or other. [Report of the Art Reference Department of Pratt Institute Free Library for year ending June 30, 1937]