# tunnel

/ˈtənəɫ/ (US) · /tˈʌnəl/ (UK)

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

## Senses

### 1. underground passage

noun · CEFR B1

a long passage built under the ground, through a hill, or under a river for cars, trains, or people.

For teachers: an artificial underground or underwater passage, typically constructed for transportation or utility infrastructure.

- The train went through a long tunnel under the mountains.
- Engineers spent nearly a decade constructing the undersea tunnel to connect the two islands, overcoming significant geological challenges along the way.

### 2. animal burrow

noun · CEFR B2

a long hole in the ground made by an animal to live in or move through.

For teachers: a subterranean passage or burrow excavated by an animal for habitation or transit.

- The rabbit disappeared into a small tunnel near the edge of the field.
- The garden was riddled with complex tunnels created by moles, which had significantly damaged the root systems of the prize-winning roses.

### 3. computing

noun · CEFR C1 · Technical

a safe way to send data over the internet by hiding it inside another type of data.

For teachers: a communication protocol that allows for the movement of data from one network to another by encapsulating one protocol within another.

- He used a secure tunnel to access his office files from home.
- The network administrator established an SSH tunnel to bypass the restrictive firewall and manage the remote server securely.

### 4. to dig a passage

verb · CEFR B2

to dig a long hole under or through something.

For teachers: to excavate a tunnel through or under a physical barrier. Often used with 'through' or 'under'.

- The prisoners tried to tunnel under the wall to escape.
- The construction crew had to tunnel through solid granite to complete the new highway extension before the winter deadline.

### 5. physics

verb · CEFR C2 · Technical

when a tiny particle passes through a barrier that it normally should not be able to cross.

For teachers: to undergo the quantum-mechanical phenomenon where a particle penetrates a potential energy barrier that it classically lacks the energy to surmount.

- In quantum physics, particles can sometimes tunnel through barriers.
- Quantum tunneling is a fundamental process in nuclear fusion, allowing protons to overcome their mutual electrostatic repulsion despite having insufficient kinetic energy.

## Examples

- The train goes through a long tunnel under the mountain.
- Engineers are building a new tunnel to connect the two islands and reduce travel time for commuters.
- The construction of the subaqueous tunnel required advanced boring machines capable of maintaining structural integrity against the immense pressure of the overlying seabed.

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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.