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I looked up the synonyms of the word tunnel and came across 'shaft' in the list. However, I have never heard of a tunnel being called a shaft before.

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    Basically no two words are completely interchangeable— which is why both words exist, after all. They may be synonyms in certain contexts, but will not be in others.
    – choster
    Aug 9, 2016 at 20:14
  • books.google.com/…
    – Jim
    Aug 9, 2016 at 20:17
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    I agree that this depends on context. In certain types of fiction, tunnel and shaft are very much not the same thing—one might almost call them antonyms.
    – 1006a
    Aug 10, 2016 at 3:06
  • In railroading, a hole horizontally through a mountain was sometimes referred to as a shaft. This often came about from initially not wanting to call the two ends, not yet connected, a tunnel. If it took a long time to get completed, they would often be referring to the shaft into the mountain, and the locals might pick this up as the main term. However, this is likely a specialized case.
    – MAP
    Aug 10, 2016 at 8:59
  • Old manually dug mines often have steeply sloping tunnels/shafts where the terminology tends to be more used to refer to it's purpose. As an access tunnel gets steeper its still a tunnel, while as a shaft gets a shallower angle it's still a shaft. In the range 30-60 degrees, who knows? Aug 10, 2016 at 11:23

4 Answers 4

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Shaft: a long, narrow, typically vertical hole that gives access to a mine, accommodates a lift in a building, or provides ventilation.

Tunnel: an artificial underground passage, especially one built through a hill or under a building, road, or river.

So a shaft could form part of a tunnel, particularly an entrance, but since a tunnel provides passage through something and a shaft is usually vertical it's unlikely that a whole tunnel would be called a shaft - unless it went right through the centre of the Earth.

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    There's nothing in either definition that says they must contradict. An angular shaft into the side of a hill would be dug using a tunnel boring machine, and could entirely aptly be called a tunnel, particularly if it ended at a room or cavern. Aug 10, 2016 at 2:50
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From wikipedia:

In civil engineering a shaft is an underground vertical or inclined passageway. Shafts are constructed for a number of reasons including:

  • For the construction of a tunnel
  • For ventilation of a tunnel or underground structure
  • As a drop shaft for a sewerage or water tunnel
  • For access to a tunnel or underground structure, also as an escape route

For example, a mine shaft is a tunnel that goes down into the earth. I suppose a shaft can be considered maybe a type of tunnel. It's simply more of a vertical opening/passageway that could allow for a tunnel, ventilation unit, etc.

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Not being an engineer, looking at previous answers, I would say that whilst a shaft is typically vertical this does not stop it from being a tunnel as a tunnel can be defined as 'an artificial underground passage, especially one built through a hill or under a building, road, or river.'

As a result, a shaft could be considered a special type of tunnel. (Think of the difference between squares and rectangles - they look different but a square can be classed as a special type of rectangle (https://math.okstate.edu/geoset/Projects/Ideas/SquareRect.htm)

Looking for something a little more authoritative, How Stuff Works (http://science.howstuffworks.com/engineering/structural/tunnel.htm) states:

A tunnel is a horizontal passageway located underground...

Some structures may require excavation similar to tunnel excavation, but are not actually tunnels. Shafts, for example, are often hand-dug or dug with boring equipment. But unlike tunnels, shafts are vertical and shorter.

So, I guess my non-engineer brain is wrong: a shaft can't be a tunnel.

However, as an English teacher, I feel that the answer lies in the fact that these words are synonyms; they are similar to each other - related in some way - but are not able to be interchanged without altering an aspect of the meaning of the original sentence in some way.

Either way, you've widened the options you have to choose from when talking or writing about tunnels, vertical or otherwise, in the future!

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There is an obsolete use of tunnel, which means the same as shaft, in its context.

tunnel, Oxford English Dictionary

The shaft or flue of a chimney. Obsolete

1817 Scott Rob Roy I. v. 109 The fire..roared, blazed, and ascended, half in smoke, half in flame, up a huge tunnel, with an opening wide enough to accomodate a stone-seat within its ample vault. (emphasis added.)

Otherwise, the distinction that the other answers made, that a tunnel is horizontal and a shaft vertical is correct, although note that a tunnel may have a slope and a shaft may be slanted, as the OED states:

shaft, Oxford English Dictionary:

A vertical or slightly inclined well-like excavation made in mining, tunnelling, etc., as a means of access to underground workings, for hoisting out materials, testing the subsoil, ventilation, etc

But...see Rigzone News. The article is titled Horizontal Drilling: How Do They Get It To Go Sideways? for a diagram of what might be called a horizontal shaft, although I do not find the term in the article.

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