bulb in WordNet English dictionary

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