To free or remove (a button) from a buttonhole.(verb-transitive)
To open as if by unbuttoning: unbutton the hatches. (verb-transitive)
To undo buttons.(verb-intransitive)
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.
Use "unbutton" in a sentence
"The last straw for me came when I was ushered into a plexiglas cell in full view of the terminal, given an intimate frisk, then told to unbutton the pants, and had the guard stick his hand right down to the genitals."
"In the last couple of years, even before the underwear bomber, the searches have always involved a demand that I unbutton my pants."
"Wear them to work, or roll up the sleeves, unbutton a few buttons and party down."