What is the meaning of bulb?

noun

• A modified bud consisting of a thickened globular underground stem serving as a reproductive structure.
• Electric lamp consisting of a transparent or translucent glass housing containing a wire filament (usually tungsten) that emits light when heated by electricity.
  • synonyms: light bulb, lightbulb, incandescent lamp, electric light, electric-light bulb
• A rounded part of a cylindrical instrument (usually at one end. )
  • usage: "the bulb of a syringe"
• Anything with a round shape resembling a teardrop.
• Lower or hindmost part of the brain; continuous with spinal cord; (`bulb' is an old term for medulla oblongata. )
  • usage: "the medulla oblongata is the most vital part of the brain because it contains centers controlling breathing and heart functioning"
  • synonyms: medulla oblongata, medulla
• A rounded dilation or expansion in a canal or vessel or organ. .