Etymology
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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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acephalous (adj.)

"headless," 1731, from French acéphale + -ous or directly from Late Latin acephalus, from Greek akephalos. See a- (3) "not" + cephalo- "head."

Principally in botany and zoology, but also "without a leader" (1751). Acephali as the name of a fabulous race of men with no heads, said by ancient writers to inhabit part of Africa, is attested from c. 1600, from Late Latin plural of acephalus, from Greek akephalos; the name also appears in Church history in reference to sects that refused to have priests or bishops (1620s). Related: Acephalian (1580s); acephalic (1650s).

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acer (n.)

maple tree genus name, from Latin acer, a word of uncertain origin, perhaps from PIE *ak- "be sharp" (see acro-) and so called for its pointed leaves.

There seem to have been two roots for "maple" in Indo-European; cognates of this one are said to include Old High German ahorn "maple," and there is a similar form in Greek akastos "maple," perhaps also Hittite hiqqar- "maple." De Vaan writes, "This may well be a non-PIE tree name which was borrowed into Greek and Latin."

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acerbic (adj.)
1865, originally, and usually, figurative: "sour, harsh, severe" (of speech, manners, etc.), from Latin acerbus "harsh to the taste, sharp, bitter, sour," especially of unripe fruits, etc., also figuratively, of character, conduct, etc. (see acerbity) + -ic. The earlier adjective was simply acerb (1650s), from French acerbe, from Latin acerbus.
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acerbity (n.)
Origin and meaning of acerbity

"sourness, with roughness or astringency of taste," 1570s, from French acerbité, from Latin acerbitatem (nominative acerbitas) "harshness, sharpness, bitterness, sourness," literal and figurative (as in virus acerbitatis "the poison of malice"), from acerbus "bitter to taste, sharp, sour, tart," from Proto-Italic *akro-po- "sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce").

The earliest use in English is figurative, of "sharp and bitter" persons. Of tastes, from 1610s. Latin acerbus is related to acer "sharp" as superbus "haughty" to super "above."

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acervate (v.)

"to heap up," 1610s, from Latin acervatus, past participle of acervare "to heap up," from acervus "heap," which is akin to acer "sharp" (from PIE root *ak- "be sharp, rise (out) to a point"). Related: Acervated; acervating; acerval; acervative; acervuline "occurring in clusters; clustered" (by 1859).

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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"). Compare acervate.

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acescent (adj.)

"becoming sour," 1670s, from French acescent, from Latin acescentem (nominative acescens), present participle of acescere "become sour," from acer "sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce").

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acetaminophen (n.)
U.S. name for "para-acetylaminophenol," 1960, composed of syllables from the chemical name: acetyl, a derivative of acetic (q.v.; also see acetylene) + amino- + phenol. In Britain, the same substance is paracetamol.
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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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