a·ce·tyl (?-s?t?l, ?s??-tl)n. The methyl acyl group, CH3CO, formally derived from acetic acid.ac?e·tyl?ic (?s??-t?l??k) adj.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.acetyl (?æs??ta?l; ??si?ta?l) n (Chemistry) (modifier) of, consisting of, or containing the monovalent group CH3CO-: acetyl group or radical. [C19: from acet(ic) + -yl] acetylic adjCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014a?ce?tyl (??sit l, ??s?t l, ?æs ? tl) n. the univalent group CH3CO?, derived from acetic acid. [1860?65] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.