but•ton. 1. a small disk, knob, or the like attached to an article, as of clothing, and serving as a fastener when passed through a buttonhole or loop. 2. anything resembling a button, esp. in being small and round, as a candy, ornament, or marker. 3. a badge or emblem bearing a name, slogan, or the like, for wear on the lapel, dress, etc.: campaign buttons. 4. a small knob or disk pressed to activate an electric circuit, operate a machine, open a door, etc. 5.