n.1. Botany a. A short, modified, underground stem surrounded by usually fleshy modified leaves that contain stored food for the shoot within: an onion bulb; a tulip bulb.
b. A similar underground stem or root, such as a corm, rhizome, or tuber.
c. A plant that grows from a bulb.
2. A rounded projection or part: the bulb of a syringe.
3. A light bulb.
4. Anatomy A rounded dilation or expansion of a canal, vessel, or organ.