Having the ends of the collar fastened down by buttons: a button-down shirt.
Conservative, conventional, or unimaginative: "a colorful character in the buttoned-down, dull-gray world of business” ( Newsweek).
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.