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.
1808 (in acetic acid), from French acétique "pertaining to vinegar, sour, having the properties of vinegar," from Latin acetum "vinegar" (properly vinum acetum "wine turned sour;" see vinegar), originally the past participle of acere "be sharp; be sour" (related to acer "sharp," from PIE root *ak- "be sharp, rise (out) to a point, pierce").
"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).
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.
"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."