# sea

/ˈsi/ (US) · /sˈiː/ (UK)

Source: https://englishreference.com/word/sea
Updated: 2026-06-19

## Senses

### 1. the ocean

noun · CEFR A1

the large body of salt water that covers most of the Earth.

For teachers: the expanse of salt water that covers most of the Earth's surface and surrounds its landmasses.

- The children spent the whole afternoon swimming in the sea.
- The fishing fleet returned to the harbour just as the sea began to turn a deep, stormy grey under the gathering clouds.

Usage: Often used with the definite article 'the'.

### 2. a large amount

noun · CEFR B2

a very large number or amount of something that looks like it has no end.

For teachers: a vast or overwhelming quantity of something, used figuratively to suggest immense scale or movement.

- Looking out from the stage, the singer saw a sea of happy faces.
- The protesters formed a sea of umbrellas in the square, shielding themselves from the relentless autumn rain while they waited for the announcement.

Usage: Usually follows the pattern 'a sea of [noun]'.

### 3. rough water or waves

noun · CEFR B2

the movement of the water, especially when it is rough or has big waves.

For teachers: the state of the water's surface in terms of waves and swell, often used in the plural to describe rough conditions.

- The small boat struggled to stay upright in the heavy seas.
- The captain decided to change course to avoid the high seas reported by the weather station further north.

Usage: Often used in the plural ('heavy seas') to describe weather conditions.

### 4. lunar plain

noun · CEFR C2 · Technical

a large, dark, flat area on the surface of the moon.

For teachers: a large, dark basaltic plain on Earth's Moon, historically mistaken for a body of water.

- The Sea of Tranquility is the most famous dark plain on the moon.
- Early astronomers named these vast basaltic plains 'seas' under the mistaken belief that they were filled with water rather than volcanic rock.

Usage: Often translated from the Latin 'mare'.

Teaching tip: This is a specialized term used in astronomy; students will mostly encounter it in textbooks about space.

### 5. particle physics

noun · CEFR C2 · Technical

a group of particles that constantly appear and disappear inside an atom.

For teachers: a theoretical model of the vacuum or the interior of a hadron consisting of a constant flux of virtual particles.

- Scientists study the sea of quarks to understand how atoms work.
- The distribution of momentum among the sea quarks provides crucial data for high-energy collision experiments in particle accelerators.

Usage: Used specifically in quantum field theory and particle physics.

## Examples

- The ship sails on the sea.
- We spent the afternoon swimming in the warm sea.
- The old lighthouse stood as a lonely sentinel against the fury of the winter sea.

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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.