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bulb

n. · v.
US //ˈbəɫb// UK //bˈʌlb// bulb
  1. 1 light bulb (n.)
    A2 Elementary

    the glass part of an electric lamp that produces light.

    the glass housing of an incandescent or LED lamp that emits light when powered.

    Example

    The light bulb in the hallway burned out, so we need to buy a new one.

    Example

    The energy-efficient LED bulb provides the same level of brightness as a traditional hundred-watt incandescent while consuming significantly less power.

    Usage

    Often used in the compound 'light bulb'.
  2. 2 plant part (n.)
    B1 Intermediate Science

    the round underground part of some plants, like onions or tulips, where they store food.

    a rounded underground storage organ in plants, consisting of a short stem covered by fleshy leaves.

    Example

    You should plant the tulip bulbs in the autumn so they flower in the spring.

    Example

    The gardener carefully separated the lily bulbs to ensure each one had enough space to develop its own root system before the first frost.

    Usage

    Commonly used in gardening and botany contexts.
    • corm
    • tuber
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  1. 3 rounded shape (n.)
    B2 Upper Intermediate

    any object that is round at one end and thinner at the other.

    a rounded, protuberant part of an object or anatomical structure.

    Example

    The thermometer has a small glass bulb at the bottom filled with red liquid.

    Example

    The glassblower carefully shaped the bulb of the wine glass, ensuring the walls were of uniform thickness throughout the curve.
  2. 4 ship's bow (n.)
    C2 Proficiency Technical Science

    a rounded part at the front of a ship below the water that helps it move faster.

    a bulbous protuberance at the bow of a vessel, designed to modify the water flow and reduce drag.

    Example

    The large ship has a bulb at the front to help it save fuel.

    Example

    The installation of a bulbous bow significantly improved the tanker's fuel efficiency by reducing wave-making resistance during long-haul voyages.

    Usage

    Usually refers to a 'bulbous bow' in naval architecture.

    Teacher's tip

    This is a highly specialized term; learners are unlikely to encounter it outside of maritime engineering.
    • bulbous bow
  3. 5 to swell (v.)
    C2 Proficiency Literary

    to swell or grow into a round shape.

    to take the shape of a bulb or to swell into a protuberance.

    Example

    The base of the plant began to bulb as it matured.

    Example

    The glass began to bulb outward under the pressure of the artisan's breath, glowing a fierce orange in the dim workshop.

    Usage

    Intransitive verb.

    Teacher's tip

    This verbal use is rare and mostly found in older literature or technical descriptions of growth.
Origin

Etymology tree Ancient Greek βολβός (bolbós)bor. Latin bulbusder. English bulb Inherited from Middle English bulb, bolbe, from Latin bulbus (“bulb, onion”), from Ancient Greek βολβός (bolbós, “plant with round swelling on underground stem”).

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