<p><strong>Noun</strong></p><ul><li>A small disk, knob, or the like for sewing or otherwise attaching to an article, as of clothing, serving as a fastening when passed through a buttonhole or loop.</li><li>Anything resembling a button, especially in being small and round, as any of various candies, ornaments, tags, identification badges, reflectors, markers, etc.</li><li>A badge or emblem bearing a name, slogan, identifying figure, etc., for wear on the lapel, dress, etc.: campaign buttons.</li><li>Any small knob or disk pressed to activate an electric circuit, release a spring, or otherwise operate or open a machine, small door, toy, etc.</li><li>Botany: a bud or other protuberant part of a plant.</li><li>Mycology: a young or undeveloped mushroom.</li><li>Any protuberant part of a fungus.</li><li>Zoology: any of various small parts or structures resembling a button, as the rattle at the tip of the tail in a very young rattlesnake.</li><li>Boxing (Informal): the point of the chin.</li><li>Also called turn button: a fastener for a door, window, etc., having two arms and rotating on a pivot that is attached to the frame.</li><li>Metallurgy: (in assaying) a small globule or lump of metal at the bottom of a crucible after fusion.</li><li>Fencing: the protective, blunting knob fixed to the point of a foil.</li><li>Horology: crown (def 19).</li><li>Computers: (in a graphical user interface) a small, button-shaped or clearly defined area that the user can click on or touch to choose an option.</li></ul><p><strong>Verb</strong></p><ul><li>(Used with object) to fasten with a button or buttons: She quickly buttoned her coat.</li><li>To insert (a button) in a buttonhole or loop: He buttoned the top button of his shirt.</li><li>To provide (something) with a button or buttons.</li><li>(Used without object) to be capable of being buttoned: This coat buttons, but that one zips.</li></ul>