"act or condition of going faster," 1530s, from Latin accelerationem (nominative acceleratio) "a hastening," noun of action from past-participle stem of accelerare "to hasten, quicken," from ad "to" (see ad-) + celerare "hasten," from celer "swift," which is perhaps from PIE *keli- "speeding" (see celerity).

"non-Catholic," 1809, from a- (3) + Catholic.

1868, earlier alla capella (1824), from Italian, "in the style of Church music, in the manner of the chapel," literally "according to the chapel," from cappella "chapel" (see chapel). Originally in reference to older church music (pre-1600) which was written for unaccompanied voices; applied 20c. to unaccompanied vocal music generally. Italian a is from Latin ad "to, toward; for; according to" (see ad-); alla is a la "to the." Sometimes in the Latin form a capella. Also denoting "that instruments are to play in unison with the voices, or that one part is to be played by a number instruments." ["Chambers's Encyclopaedia," 1868]You are not the first person puzzled by the expression "A Capella," or, at any rate, unable to understand it should signify the exact reverse of what it literally does signify. The chorales in oratorios were invariably accompanied, either by double-bass or the whole band. Hence they were, with perfect correctness, said to be performed "a capella." But, as other chorales, sung as part of the church service, were written in the same and simple style the expression "a capella" came in time to be applied to them also, despite their being sung without any instrumental accompaniment whatever. [The Music World, Sept. 11, 1875]

in zoology, "having a spiny head," 1847, from acantho- (see acanthus) + Latinized adjectival form of Greek kephalē "head" (see cephalo-) + -ous.

"native or inhabitant of the French colony of Acadia" in what is now the Canadian Maritimes, 1705, from Acadia, Latinized form of Acadie, French name of Nova Scotia, probably from Archadia, the name given to the region by Verrazano in 1520s, from Greek Arkadia, then emblematic in pastoral poetry of a place of rural peace (see Arcadian); the name may have been suggested to Europeans by the native Micmac (Algonquian) word akadie "fertile land." The Acadians, expelled by the English in 1755, settled in large numbers in Louisiana, and were known there as Acadians by 1803 (see Cajun, which is a corruption of Acadian).

mid-15c., Achademie, "the classical Academy," properly the name of the public garden where Plato taught his school, from Old French (Modern French Académie) and directly from Latin Academia, from Greek Akadēmeia "The Academy; the grove of Akadēmos," a legendary Athenian of the Trojan War tales (his name, Latinized as Academus, apparently means "of a silent district"), who was original estate-holder of the site.The A[cademy], the Garden, the Lyceum, the Porch, the Tub, are names used for the five chief schools of Greek philosophy, their founders, adherents, & doctrines: the A., Plato, the Platonists & Platonism; the Garden, Epicurus, the Epicureans, & Epicureanism; the Lyceum, Aristotle, the Aristotelians, & Aristotelianism; the Porch, Zeno, the Stoics, & Stoicism; the Tub, Antisthenes, the Cynics, & Cynicism. [Fowler] Compare lyceum. By 1540s the word in English was being used for any school or training place for arts and sciences or higher learning. "In the 18th century it was frequently adopted by schools run by dissenters, and the name is often found attached to the public schools in Scotland and Northern Ireland" [Encyclopaedia Britannica, 1941]; hence, in the U.S., a school ranking between an elementary school and a university. "In England the word has been abused, and is now in discredit in this sense" [OED]. By 1560s it was used for "a place of training" in any sense (riding schools, army colleges). The word also was used of associations of adepts for the cultivation and promotion of some science or art, whether founded by governments, royalty, or private individuals. Hence Academy award (1939), so called for their distributor, the U.S.-based Academy of Motion Picture Arts and Sciences (founded 1927).