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").
before vowels acet-, word-forming element from acetic and generally indicating compounds from or related to acetic acid, thus ultimately from Latin acetum "vinegar."
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.
aspirated form of ah; in English often used in representations of German or Celtic speech.
name of the armor-bearer and faithful friend of Aeneas in the "Aeneid;" The phrase fidus Achates was proverbial for "faithful friend, loyal and devoted companion." The name is from Greek akhatēs "agate" (see agate).
Middle English aken, from Old English acan "suffer continued pain," from Proto-Germanic *akanan, which is perhaps from a PIE root *ag-es- "fault, guilt," with apparent cognates in Sanskrit and Greek, which itself is perhaps imitative of groaning.
Originally the verb was pronounced "ake," the noun "ache" (as in speak/speech). The noun changed its pronunciation to conform to the verb, but the spelling of both was changed to ache c. 1700 on a false assumption of a Greek origin (specifically Greek akhos "pain, distress," which rather is a distant relation of awe (n.)). Related: Ached; aching.