# bulb

/ˈbəɫb/ (US) · /bˈʌlb/ (UK)

Source: https://englishreference.com/word/bulb
Updated: 2026-06-20

## Senses

### 1. light bulb

noun · CEFR A2

the glass part of an electric lamp that produces light.

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

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

noun · CEFR B1

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

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

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

### 3. rounded shape

noun · CEFR B2

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

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

- The thermometer has a small glass bulb at the bottom filled with red liquid.
- The glassblower carefully shaped the bulb of the wine glass, ensuring the walls were of uniform thickness throughout the curve.

### 4. ship's bow

noun · CEFR C2 · Technical

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

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

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

Teaching tip: This is a highly specialized term; learners are unlikely to encounter it outside of maritime engineering.

### 5. to swell

verb · CEFR C2 · Literary

to swell or grow into a round shape.

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

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

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

## Examples

- I need to change the light bulb in the kitchen.
- We spent the afternoon planting tulip bulbs in the garden so they would bloom by early spring.
- The inventor experimented with hundreds of different filaments before finding a material that would glow reliably inside the vacuum of a glass bulb.

---

From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.