Definition of: bulb

(bulb) noun
1. Bot. a A leaf bud comprised of a cluster of thickened, scalelike leaves, growing usually underground and sending forth roots from the lower face, as the onion or lily, b Any of several underground stems resembling bulbs, as the corm of a crocus or a dahlia tuber.
2. Any protuberance resembling a plant bulb, as the bulb at the root of a hair (see illustration under HAIR), the enlarged end of a thermometer tube, etc.
3. Electr. An evacuated glass container holding the filament of an incandescent electric light.
4. A vacuum tube.
5. Anat. The medulla oblongata. [<L bulbus <Gk. bolbos bulbous root]
—bul·ba·ceous (bul·bā′·shəs) adjective
—bul′bous adjective