Etymology
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aculeate (adj.)

c. 1600, figurative, "pointed, stinging," of writing, from Latin aculeatus "having a sting; thorny, prickly," also figurative, from aculeus "a sting, prickle," diminutive of acus "a needle" (from PIE root *ak- "be sharp, rise (out) to a point, pierce"). From 1660s in a literal sense, in zoology, "furnished with a sting;" by 1870 in botany.

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acumen (n.)

"quickness of perception, keen insight," 1530s, from Latin acumen "a point, sting," hence, figuratively, "mental sharpness, shrewdness," from acuere "to sharpen," literal and figurative (of intellect, emotion, etc.), related to acus "a needle" (from PIE root *ak- "be sharp, rise (out) to a point, pierce"). Related: Acuminous.

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acuminate (adj.)

1640s, "having a long, tapering end" (of certain feathers, leaves, etc.), from Latin acuminatus, past participle of acuminare "to sharpen," from acumen "a point" (see acumen). Related: Acuminated; acumination.

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acupressure (n.)

1859, name of a method (developed by J.Y. Simpson) of stopping surgical bleeding by pinning or wiring the artery shut, from Latin acus "a needle" (from PIE root *ak- "be sharp, rise (out) to a point, pierce") + pressure (n.). From 1958 in reference to the oriental body therapy also known as shiatsu (said to mean literally "finger-pressure" in Japanese).

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acupuncture (n.)

1680s, "pricking with a needle" as a surgical operation to ease pain, from Latin acus "a needle" (from PIE root *ak- "be sharp, rise (out) to a point, pierce") + puncture. The verb is recorded by 1972.

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acupuncturist (n.)

"one who practices acupuncture," 1843, from acupuncture + -ist.

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acute (adj.)

late 14c., originally of fevers and diseases, "coming quickly to a crisis" (opposed to chronic), from Latin acutus "sharp, pointed," figuratively "shrill, penetrating; intelligent, cunning," past participle of acuere "to sharpen" (literal and figurative), from PIE root *ak- "be sharp, rise (out) to a point, pierce."

It was also used of humors (early 15c.). The meaning "ending in a sharp point" is from 1560s; the sense of "sharp or penetrating in intellect" is from 1580s. Of feelings, pains, etc., "intense," 1727. As a noun, early 15c. of fevers; c. 1600 as "an acute accent." Related: Acutely; acuteness.

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-acy 

word-forming element making nouns of quality, state, or condition, a confusion in English of three similar suffixes from Latin:

1. in primacy, etc., from Old French -acie and directly from Medieval Latin -acia, Late Latin -atia, making nouns of quality, state, or condition from nouns in -as.

2. in advocacy, etc., from Late Latin -atia, forming nouns of state from nouns in -atus.

3. in fallacy, etc., from Latin -acia, forming nouns of quality from adjectives in -ax (genitive -acis). Also forming part of -cracy. It has been extended in English to nouns not found in Latin (accuracy) and to non-Latin words (piracy).

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A.D. 

1570s, an abbreviation of Latin anno Domini "year of the Lord." This system of counting years was put forth by Dionysius Exiguus in 527 or 533 C.E., but used at first only for Church business. Introduced in Italy in 7c., France (partially) in 8c. In England, first found in a charter of 680 C.E. Ordained for all ecclesiastical documents in England by the Council of Chelsea, July 27, 816.

The resistance to it might have come in part because Dionysius chose 754 A.U.C. as the birth year of Jesus, while many early Christians would have thought it was 750 A.U.C. (See John J. Bond, "Handy-Book of Rules and Tables for Verifying Dates With the Christian Era," 4th ed., London: George Bell & Sons, 1889.) There is a use of simple a for anno domini in an English document from c. 1400; A.C., for Anno Christi, also was common 17c.

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ad- 

word-forming element expressing direction toward or in addition to, from Latin ad "to, toward" in space or time; "with regard to, in relation to," as a prefix, sometimes merely emphatic, from PIE root *ad- "to, near, at."

Simplified to a- before sc-, sp- and st-; modified to ac- before many consonants and then re-spelled af-, ag-, al-, etc., in conformity with the following consonant (as in affection, aggression). Also compare ap- (1).

In Old French, reduced to a- in all cases (an evolution already underway in Merovingian Latin), but French refashioned its written forms on the Latin model in 14c., and English did likewise 15c. in words it had picked up from Old French. In many cases pronunciation followed the shift.

Over-correction at the end of the Middle Ages in French and then English "restored" the -d- or a doubled consonant to some words that never had it (accursed, afford). The process went further in England than in France (where the vernacular sometimes resisted the pedantic), resulting in English adjourn, advance, address, advertisement (Modern French ajourner, avancer, adresser, avertissement). In modern word-formation sometimes ad- and ab- are regarded as opposites, but this was not in classical Latin.

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