noun

1. any small disk, knob, etc. used as a fastening or ornament, as one put through a buttonhole on a garment
2. anything small and shaped like a button; specif.,
   1. a small emblem of membership, distinction, etc., generally worn in the lapel
   2. a small knoblike part, as a bud on a plant or the end of a rattlesnake's rattles
   3. a small knoblike part that is pushed or turned to operate a doorbell, electric lamp, etc.
   4. a guard on the tip of a fencing foil
   5. a small, immature mushroom
3. ☆ Slang the point of the chin

Etymology: ME botoun < OFr boton, a button, bud < buter: see butt

transitive verb, intransitive verb

1. to fasten with or as with a button or buttons
2. to provide or be provided with a button or buttons