but·ton-down (b?t?n-doun?)adj.1. Having buttons extending down the front from the collar to the waist: a button-down shirt.2. Fastened down by buttons: a button-down collar.3. also but·toned-down (b?t?nd-) Conservative, conventional, or unimaginative: “a colorful character in the buttoned-down, dull-gray world of business” (Newsweek).n. A button-down shirt.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.button-down adj 1. (Clothing & Fashion) (of a collar) having points that are fastened to the garment with buttons 2. (Clothing & Fashion) (of a shirt) having a button-down collar 3. (Clothing & Fashion) Also: buttoned-down conventional or conservative: a button-down corporate culture. Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014but?ton-down` adj. 1. (of a collar) having buttonholes at the ends with which it can be buttoned to the front of the garment. 2. (of a garment) having a button-down collar. 3. Also, but?toned down?. conventional, unimaginative, or conservative. [1930?35, Amer.] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.