From Longman Dictionary of Contemporary Englishbulbbulb /bʌlb/ ●●○ noun [countable] 1 
DTthe glass part of an electric light, that the light shines from SYN light bulb a 100-watt bulb2 HBPa root shaped like a ball that grows into a flower or plant tulip bulbs
DTthe glass part of an electric light, that the light shines from SYN light bulb a 100-watt bulb2 HBPa root shaped like a ball that grows into a flower or plant tulip bulbsExamples from the Corpus
bulb• Before buying, check that maintenance and bulb cleaning can be carried out easily and safely.• Which leads to the brightest bulb in the Sheffield chandelier of pop, the Longpigs.• An outside cistern could be kept from freezing by hanging a light bulb near it and leaving it on all the time.• They stole my narcissus bulbs that I had been so carefully forcing to bloom in January.• Halogen lamps give excellent service, hut the bulbs are fairly expensive to replace.• I was lying there, thinking that the bulb needed changing, the ceiling could use another coat.Origin bulb (1500-1600) Latin bulbus, from Greek bolbos “plant with a bulb” 